show the real content, instead of 2nd time morphing without the custom f...

...ormatter

https://github.com/dingo/api/issues/139

I'm not sure if it's the only place where it should be updated, but before that the content was generated fine, but during the

~~~php
return $response->getOriginalContent();
~~~

It was returned as collection or model and then double morphed, without the custom formatters.