Added required "main" property to bower.json

The "main" property is required for build tools like brunch or grunt otherwise you get errors like this:

```
25 Mar 14:45:37 - error: [Error: Component JSON file "/home/ed/client/bower_components/ember-sockets/.bower.json" must have `main` property. See https://github.com/paulmillr/read-components#README]
```