Path to main missing in bower.json

After attempting to `grunt bower-install` this component, I received the following error:
> angular-activerecord was not injected in your file.
Please go take a look in "app/bower_components/angular-activerecord" for the file you need, then manually include it in your file.

Adding `"main": "src/angular-activerecord.js"` to the `.bower.json` file allows the component to install properly. This pull request updates the `bower.json` file, from which `.bower.json` is generated, to include this value.