add redis cache and heroku config

Gemfile

@@ -21,6 +21,8 @@ gem 'webpacker', '~> 5.0'
 gem 'turbolinks', '~> 5'
 # Use Redis adapter to run Action Cable in production
 gem 'redis', '~> 4.2.5'
+# Ruby wrapper for hiredis (protocol serialization/deserialization and blocking I/O)
+gem 'hiredis', '~> 0.6.3'
 # Use Active Model has_secure_password
 gem 'bcrypt', '~> 3.1.7'
 # Flexible authentication solution for Rails with Warden