Travisdouce/do not return active model serializer json

Yes, that is a good thought. My initial implementation did just that. It looked like:

```ruby
class User
  include ActiveModel::Model
  attr_accessor :first_name, :attributes

  def initialize(attributes={})
    @attributes = attributes
  end
end

class FactoryGirl
  def self.create(factory, opts = {})
    User.new(opts)
  end

  def self.factories
    [
      OpenStruct.new('name' => 'Sam'),
      OpenStruct.new('name' => 'Pete')
    ]
  end
end
```
Ultimately, I think it is more robust test suite to:

1. Add `factory_girl_rails` as a development dependency
2. Create a `user` resource in the dummy app
4. Define a `user` factory in the dummy app

and test the full stack rather than implementing the `User` and `FactoryGirl` interfaces in the test suite. This might add a bit of complexity because someone would have to do a bit more sleuthing to figure out where `User` and `user` factory are defined. However, defining the `User` and `user` factory in the dummy app follows common Rails conventions, so hopefully they will not be too hard to track down.

If this ends up being the wrong decision, we can always refactor:)