Update rubocop to version 0.21.0

.rubocop.yml

@@ -3,6 +3,7 @@ AllCops:
     - 'Gemfile'
     - 'Rakefile'
   Exclude:
+    - 'bin/*'
     - 'db/schema.rb'
 
 # Avoid long parameter lists

Gemfile.lock

@@ -145,9 +145,9 @@ GEM
     remotipart (1.2.1)
     rest-client (1.6.7)
       mime-types (>= 1.16)
-    rubocop (0.20.1)
+    rubocop (0.21.0)
       json (>= 1.7.7, < 2)
-      parser (~> 2.1.7)
+      parser (~> 2.1.9)
       powerpack (~> 0.0.6)
       rainbow (>= 1.99.1, < 3.0)
       ruby-progressbar (~> 1.4)

config/initializers/cookies_serializer.rb

@@ -1,3 +1,3 @@
 # Be sure to restart your server when you modify this file.
 
-Rails.application.config.action_dispatch.cookies_serializer = :json
+Rails.application.config.action_dispatch.cookies_serializer = :json

db/migrate/00000000000002_add_devise_to_users.rb

@@ -6,18 +6,18 @@ class AddDeviseToUsers < ActiveRecord::Migration
       t.string :encrypted_password, null: false, default: ''
 
       ## Recoverable
-      t.string   :reset_password_token
+      t.string :reset_password_token
       t.datetime :reset_password_sent_at
 
       ## Rememberable
       t.datetime :remember_created_at
 
       ## Trackable
-      t.integer  :sign_in_count, default: 0, null: false
+      t.integer :sign_in_count, default: 0, null: false
       t.datetime :current_sign_in_at
       t.datetime :last_sign_in_at
-      t.string   :current_sign_in_ip
+      t.string :current_sign_in_ip
-      t.string   :last_sign_in_ip
+      t.string :last_sign_in_ip
 
       ## Confirmable
       # t.string   :confirmation_token