Do not modify built-in objects

[wKich]

https://github.com/beautify-web/js-beautify/blob/master/js/lib/beautify.js#L93-L107

Your library is not polyfill and it should not modify environment.

1. May be you don't need Object.values at all in your code. I found only one place where it use and can be simply replaced to Object.keys equivalent.
2. Or you can notify users, that them need to import Object.values polyfill manually.

I think first option is better.

[bitwiseman]

@wKich - It doesn't quite work as Object.keys, but adding an array is fine.