* [gapi.auth2] Fix parameter type of callback
According to the [documentation][]:
> The function called with the `GoogleAuth` object when it is fully
> initialized.
[documentation]: https://developers.google.com/identity/sign-in/web/reference#googleauththenoninit-onerror
* [gapi.auth2] Convert documentation to type
Types are better than description in documentation.
* [gapi.auth2] Add parameter to `gapi.auth2.init()`
See [official documentation][].
[official documentation]: https://developers.google.com/identity/sign-in/web/reference#gapiauth2initparams
* [gapi.auth2] Fix indentation
This change is best viewed with "histogram" or "patience" diffing
algorithm.
* [gapi.auth2] Add test and fix a bug
* [gapi.auth2] Add linting
