Refactoring the code for pub sub (#155)

- We were using the attribute name 'channel' to store pubsub tokens, which was confusing.
- switched to faker from ffaker
- spec for contact.rb

Gemfile.lock

@@ -186,9 +186,10 @@ GEM
     factory_bot_rails (5.1.1)
       factory_bot (~> 5.1.0)
       railties (>= 4.2.0)
+    faker (2.1.2)
+      i18n (>= 0.8)
     faraday (0.16.2)
       multipart-post (>= 1.2, < 3)
-    ffaker (2.13.0)
     ffi (1.11.1)
     figaro (1.1.1)
       thor (~> 0.14)
@@ -435,7 +436,7 @@ DEPENDENCIES
   devise_token_auth!
   facebook-messenger (~> 0.11.1)
   factory_bot_rails
-  ffaker
+  faker
   figaro
   foreman
   hashie