feature_request(update): ECMAScript 11 support

[Kristinita]

1. Summary

It would be nice if coffee-jshint will support features that introduced to ECMAScript 7 and higher.

2. Details

When I tried to run coffee-jshint for my .coffee files, I get errors like this:

125:27: 'async functions' is only available in ES8 (use 'esversion: 8').

I can’t find how I can fix it. Syntax like coffee-jshint --options esversion=11 isn’t valid. If I understood the documentation correctly, coffee-jshint users can’t set the value more than 6 for the esversion key. JSHint supports features for ECMAScript 11, and it would be nice if coffee-jshint will support them too.

3. “.jshintrc” support

In my opinion it would be nice if coffee-jshint will support the value of the esversion key from .jshintrc file. If user has "esversion": 11, it would be nice if coffee-jshint will support ECMAScript 11.

Thanks.