move cors controller to use method level respond_to so responders gem isnt a dependency for apps running rails >= 4.2

Author: DanielNill

app/controllers/attachinary/cors_controller.rb

@@ -1,9 +1,10 @@
 module Attachinary
   class CorsController < Attachinary::ApplicationController
-    respond_to :json
 
     def show
-      respond_with request.query_parameters, :content_type => 'text/plain'
+      respond_to do |format|
+        format.json { render json: request.query_parameters, content_type: "text/plain" }
+      end
     end
   end
 end