Updated to work with the latest version of Browserify

Partly fixes #98

I think this is actually a breaking change because Browserify no longer bundles .coffee files out of the box, so anyone using the BrowserifyAsset to serve .coffee files would be hosed.

One thing I wanted to mention was I wasn't sure what to do on line 25 of `lib/modules/browserify.coffee` if an error was passed to the callback.  Any suggestions?