Docblock fix in FractalTransformer

Fixed the reference to ```\League\Fractal\Resource\Collection```.
Add a a ResponseFactory::created() method to respond with a 201 Created header.
The method can accept an optional parameter to add an extra Location header.
Merge pull request #199 from ipalaus/feature/created-response

Add a ResponseFactory::created() method to respond with a 201 Created
Merge pull request #196 from ipalaus/patch-1

Docblock fix in FractalTransformer