Added loading of JSHint config

Hey,

I've noticed that this feature was missing (https://github.com/addyosmani/sublime-fixmyjs/issues/2) and I really needed this feature, so i did my best and implemented it.
If it needs more polishing, just say :-)
you can drop the `opts` here: https://github.com/sindresorhus/atom-fixmyjs/blob/03b7d503e1e817699d1da5647e9a4fdcc2b8e5f2/index.js#L20-L24