[test] fix race condition in issue4164-close-not-quit on OSX

[docs] building Node in nw19

fixed `show_in_taskbar` option for `nw.Window.open`

fixed nwjs#4970

Revert "[test] added a test case for cookie lost after devtools closed"

This reverts commit e603924.

[test] fix race condition in issue4286-inject-start-end

bump version to 0.18.7

[doc] updated docs for rebuilding native modules

Use `npm_config_` environments to override default behaviors of
npm and node-gyp. `npm_config_node_gyp` can be used to replace
`node-gyp` with `nw-gyp` during `npm install`.

Fix nwjs#5377: Gamepad API not working

upload nw19 headers

[test] add 4 test cases for worker

* process.stdout error when worker is exited
* require external modules failed in worker
* node in sharedworker
* stream events not fired in DOM when worker enabled
* stream_wrap failed in worker