add redis cache and heroku config

config/environments/production.rb

@@ -56,7 +56,7 @@ Rails.application.configure do
   config.log_tags = [ :request_id ]
 
   # Use a different cache store in production.
-  # config.cache_store = :mem_cache_store
+  config.cache_store = :redis_cache_store, { url: ENV['REDIS_URL'] }
 
   # Use a real queuing backend for Active Job (and separate queues per environment).
   # config.active_job.queue_adapter     = :resque