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Spelling for mime type. 

Do we need the content_type params in here? Controller specs bypass the rails router - [requests specs don't](https://github.com/zooniverse/Panoptes/blob/master/spec/requests/v1/api_versioning_spec.rb) and all api response content type is implicit via the [versionist accept route params](https://github.com/zooniverse/Panoptes/blob/master/config/routes.rb#L10).