Add index.js to project root to make angular-bugsnag browserify ready

Could you add the following code as index.js in the project root

```
require('./dist/angular-bugsnag');
module.exports = 'angular-bugsnag';
```

This will make your package browserify ready to use like...

```
angular.module('myapp', [require('angular-bugsnag')]);
```

This is the way all the Angular modules are set up since they started supporting browserify.
