Bump chai from 4.1.2 to 4.2.0 (improbable-eng#308)

Bumps [chai](https://github.com/chaijs/chai) from 4.1.2 to 4.2.0.
<details>
<summary>Release notes</summary>

*Sourced from [chai's releases](https://github.com/chaijs/chai/releases).*

> ## 4.2.0 / 2018-09-25
> This is a minor release. Thank you to all of our contributors and users!
> 
> # New Features
> * feat(assertions): add 'still' language chain ([#1194](https://github-redirect.dependabot.com/chaijs/chai/issues/1194); [**ScottRudiger**](https://github.com/ScottRudiger))
> * .lengthOf for Maps and Sets ([improbable-eng#1110](https://github-redirect.dependabot.com/chaijs/chai/issues/1110), [improbable-eng#1131](https://github-redirect.dependabot.com/chaijs/chai/issues/1131); [**asbish**](https://github.com/asbish))
> * feat: Add the assert.fail([message]) interface ([improbable-eng#1116](https://github-redirect.dependabot.com/chaijs/chai/issues/1116), [improbable-eng#1117](https://github-redirect.dependabot.com/chaijs/chai/issues/1117); [**s-leroux**](https://github.com/s-leroux))
> 
> # Bug Fixes
> * fix: remove Chai frames from `.deep.equal` stack ([improbable-eng#1124](https://github-redirect.dependabot.com/chaijs/chai/issues/1124); [**meeber**](https://github.com/meeber))
> * add 'catch' keyword to proxyExcludedKeys ([improbable-eng#1050](https://github-redirect.dependabot.com/chaijs/chai/issues/1050), [improbable-eng#1101](https://github-redirect.dependabot.com/chaijs/chai/issues/1101); [**generalandrew**](https://github.com/generalandrew))
> * property assertion should only accept strings if nested ([improbable-eng#1043](https://github-redirect.dependabot.com/chaijs/chai/issues/1043), [improbable-eng#1044](https://github-redirect.dependabot.com/chaijs/chai/issues/1044); [**solodynamo**](https://github.com/solodynamo))
> * fix: Make tests pass with `--use_strict` ([improbable-eng#1034](https://github-redirect.dependabot.com/chaijs/chai/issues/1034), [improbable-eng#1040](https://github-redirect.dependabot.com/chaijs/chai/issues/1040); [**shvaikalesh**](https://github.com/shvaikalesh))
> 
> # Performance
> * perf: Optimize proxify and stringDistance ([improbable-eng#1098](https://github-redirect.dependabot.com/chaijs/chai/issues/1098); [**sophiebits**](https://github.com/sophiebits))
> * fix: Avoid repeated String#slice calls in stringDistance ([improbable-eng#1095](https://github-redirect.dependabot.com/chaijs/chai/issues/1095); [**bmeurer**](https://github.com/bmeurer))
> 
> # Style
> * Fix typos and remove trailing whitespaces ([improbable-eng#1042](https://github-redirect.dependabot.com/chaijs/chai/issues/1042); [**simonewebdesign**](https://github.com/simonewebdesign))
> * Remove unnecessary code ([improbable-eng#1049](https://github-redirect.dependabot.com/chaijs/chai/issues/1049); [**abetomo**](https://github.com/abetomo))
> * Fix variable declaration ([improbable-eng#1048](https://github-redirect.dependabot.com/chaijs/chai/issues/1048); [**abetomo**](https://github.com/abetomo))
> 
> # Tests
> * test(assert): increase coverage ([improbable-eng#1084](https://github-redirect.dependabot.com/chaijs/chai/issues/1084), [improbable-eng#1085](https://github-redirect.dependabot.com/chaijs/chai/issues/1085); [**brutalcrozt**](https://github.com/brutalcrozt))
> * test: stop modifying globals in Proxy tests ([improbable-eng#1144](https://github-redirect.dependabot.com/chaijs/chai/issues/1144); [**meeber**](https://github.com/meeber))
> 
> # Docs
> * Fix unbalanced quotes in assert.notInclude example ([#1200](https://github-redirect.dependabot.com/chaijs/chai/issues/1200); [**haykam821**](https://github.com/haykam821))
> * docs: fix bad `.string` example ([improbable-eng#1156](https://github-redirect.dependabot.com/chaijs/chai/issues/1156), [improbable-eng#1157](https://github-redirect.dependabot.com/chaijs/chai/issues/1157); [**meeber**](https://github.com/meeber))
> * fixed package npm url ([improbable-eng#1151](https://github-redirect.dependabot.com/chaijs/chai/issues/1151); [**wadie**](https://github.com/wadie))
> * Spelling ([improbable-eng#1145](https://github-redirect.dependabot.com/chaijs/chai/issues/1145); [**jsoref**](https://github.com/jsoref))
> * docs: corrected spelling ([improbable-eng#1141](https://github-redirect.dependabot.com/chaijs/chai/issues/1141); [**Powell-v2**](https://github.com/Powell-v2))
> * docs: fix wrong `.property` chaining examples (https://github-redirect.dependabot.com/chaijs/chai/issues/193#issuecomment-360334369, [improbable-eng#1130](https://github-redirect.dependabot.com/chaijs/chai/issues/1130); [**meeber**](https://github.com/meeber))
> * docs: improve throws examples ([improbable-eng#1113](https://github-redirect.dependabot.com/chaijs/chai/issues/1113); [**ColinEberhardt**](https://github.com/ColinEberhardt))
> * Fix typos ([improbable-eng#1107](https://github-redirect.dependabot.com/chaijs/chai/issues/1107); [**tbroadley**](https://github.com/tbroadley)) 
> * docs: correct `.ok` description ([improbable-eng#1047](https://github-redirect.dependabot.com/chaijs/chai/issues/1047); [**shvaikalesh**](https://github.com/shvaikalesh)) 
> 
> # Chores
> * chore: update package-lock.json ([#1198](https://github-redirect.dependabot.com/chaijs/chai/issues/1198); [**meeber**](https://github.com/meeber))
> * Update mocha to the latest version ([improbable-eng#1127](https://github-redirect.dependabot.com/chaijs/chai/issues/1127))
> * chore: update dependencies ([improbable-eng#1157](https://github-redirect.dependabot.com/chaijs/chai/issues/1157); [**meeber**](https://github.com/meeber))
> * Update browserify to the latest version ([improbable-eng#1135](https://github-redirect.dependabot.com/chaijs/chai/issues/1135))
> * chore: update Node versions in Travis config ([improbable-eng#1126](https://github-redirect.dependabot.com/chaijs/chai/issues/1126); [**meeber**](https://github.com/meeber))
> * chore: remove Opera from Sauce config ([improbable-eng#1125](https://github-redirect.dependabot.com/chaijs/chai/issues/1125); [**meeber**](https://github.com/meeber))
> * chore: update dependencies ([improbable-eng#1118](https://github-redirect.dependabot.com/chaijs/chai/issues/1118); [**meeber**](https://github.com/meeber))
> * chore: update dependencies ([improbable-eng#1074](https://github-redirect.dependabot.com/chaijs/chai/issues/1074); [**meeber**](https://github.com/meeber)) 
> * Chore: change coverage service (coverall to codecov) ([improbable-eng#927](https://github-redirect.dependabot.com/chaijs/chai/issues/927), [improbable-eng#1073](https://github-redirect.dependabot.com/chaijs/chai/issues/1073); [**brutalcrozt**](https://github.com/brutalcrozt))
> * chore: add package-lock.json ([improbable-eng#1013](https://github-redirect.dependabot.com/chaijs/chai/issues/1013); [**meeber**](https://github.com/meeber))
</details>
<details>
<summary>Commits</summary>

- [`26c8a79`](chaijs/chai@26c8a79) chore: [email protected] ([#1201](https://github-redirect.dependabot.com/chaijs/chai/issues/1201))
- [`ed93c93`](chaijs/chai@ed93c93) docs: fix unbalanced quotes in assert.notInclude example ([#1200](https://github-redirect.dependabot.com/chaijs/chai/issues/1200))
- [`0064f26`](chaijs/chai@0064f26) feat(assertions): add 'still' language chain ([#1194](https://github-redirect.dependabot.com/chaijs/chai/issues/1194))
- [`6da897d`](chaijs/chai@6da897d) chore: update package-lock.json ([#1198](https://github-redirect.dependabot.com/chaijs/chai/issues/1198))
- [`058ddad`](chaijs/chai@058ddad) chore(package): update mocha to version 5.0.0 ([improbable-eng#1127](https://github-redirect.dependabot.com/chaijs/chai/issues/1127))
- [`297c71a`](chaijs/chai@297c71a) Merge pull request [improbable-eng#1157](https://github-redirect.dependabot.com/chaijs/chai/issues/1157) from chaijs/fix-docs-example
- [`4584706`](chaijs/chai@4584706) docs: fix bad `.string` example
- [`651fc96`](chaijs/chai@651fc96) chore: update dependencies
- [`1021f40`](chaijs/chai@1021f40) docs: fixed package npm url ([improbable-eng#1151](https://github-redirect.dependabot.com/chaijs/chai/issues/1151))
- [`11612e9`](chaijs/chai@11612e9) test(assert): add spec with getterFn. ([improbable-eng#1085](https://github-redirect.dependabot.com/chaijs/chai/issues/1085))
- Additional commits viewable in [compare view](chaijs/chai@4.1.2...4.2.0)
</details>
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