adds .js to the extensions supported by the jsx language

[luisrudge]

fixes #144 for good

[Glavin001]

This actually will not fix the problem you are having ( #144 ), however I am merging it anyway because it will not change anything.
While the addition of the js extension is not necessary, it will not break anything because the priority of the grammar supersedes the extensions ( see https://github.com/Glavin001/atom-beautify/blob/master/src/languages/index.coffee#L86 ). The JavaScript grammar will of course be default in Atom for .js unless changed by user.

Furthermore, the real bug is #353. Basically, extensions was not working, at all. I had a couple typos. It was actually only using the grammars, for which both JavaScript (JSX) and JSX are already supported.

I will be publishing fix for #353 soon, however given any extensions are effectively useless in the currently published version, I wonder: did you test this pull request? Did it work? If so, then it was something else, such as restarting Atom or updating Atom Beautify, etc, that actually is making it work for you now, as the grammars JavaScript (JSX) and JSX were already added and usable under language JSX.

Thank you for your contributions, regardless.

[Glavin001]

Published to v0.27.4

[luisrudge]

Thanks for the explanation.