update browserify

Alright so this is actually very close to being complete, I think. I just need to create a promise for [L105](https://github.com/carrot/roots-browserify/commit/d4bd8df3a8bbfa2c528178c1e0589ed180654270#diff-2290943f47872064e53f430a293f3c8fR105), `stream.pipe`.

Basically we need to figure out how to verify browserify has completed. `bundle()` itself can return a callback, @jenius any ideas on how to convert that to a promise; I've tired `when/node.call`.
Edit: or the stream itself; I'm attempting to listen for `end` to be emitted from pipe

closes #5