Update css.js to CodeMirror Latest

I've had some trouble with this file interfering with my [lt-scss plugin](https://github.com/lambdahands/lt-scss/issues/4). Some sass functionality isn't working in the version included in LightTable such as correct nesting indentation.

I've attempted loading my own css.js file in my plugin, but the default mode overrides any files I include.

Updating the file to the latest CodeMirror version fixes my problem.