Update to LiveScript 1.3.x

Several changes since 1.2.x. See [LiveScript's changelog](http://livescript.net/#changelog) for more details.

Quick summary of important new features/changes (relevant to this plugin):

- Able to use `that` in switch statements similarly to if statements
- `for let i in array` instead of `for i in array => let`
- Key/value pairs reversed in `require!`, e.g. `require! 'module': mod` instead of `require! mod: 'module'`
- Generators now supported (keeping up with ES6 - V8 and Firefox already ship them as stable)