Fix Refresh token AbstractController::DoubleRenderError

[xkraty]

In app/controllers/api/devise/tokens_controller.rb#refresh was causing AbstractController::DoubleRenderError when access_token is revoked due to a missing return.

        if current_devise_api_refresh_token.revoked?
          error_response = Devise::Api::Responses::ErrorResponse.new(request, error: :revoked_token,
                                                                              resource_class: resource_class)

          return render json: error_response.body, status: error_response.status
        end

In spec/requests/token_spec.rb some refresh_token tests was passing access_token in headers

      before do
        post refresh_user_tokens_path, headers: authentication_headers_for(user, devise_api_token, :refresh_token), as: :json
      end

[samuelboland]

I was about to submit a PR to fix this same issue, but found this one already open. It'd be great if this could be merged.