fix: fixes bad yaml in ci config and updates tests to mock Loader (go…

…oglemaps#9)

* removes underscores from var names

* Fixes var formatting in readme and example app

* chore: Fixes var formatting in readme and example app

* test: adds codecov and readme badges

* fix: fixes link to codecov badge

* fix: updates test and release configs

* fix: updates test and release configs

* fix: fixes yaml syntax error

* fix: adds eslint deps

* fix: fixes linter errors

* fix: exports MapJSAPIOptions

* fix: adds jest config

* fix: adds missing jest dep

* fix: updates to tests

* return promise

* fix: 100% test coverage and mocking Loader

* chore: removes unneeded import in tests

* fix: resolves some minor linter errors

fix: updates build and release configs (googlemaps#8)