Point main property at src/angular-gridster.js

The main property in angular-gridster's bower.json doesn't point at a real file (there's no app/scripts folder), this points it at src/angular-gridster, as the general Bower convention is not to point at minified versions by default.

I need this so that I can use the main property to automatically include script tags in my index.html based on my dependencies' bower.json files.