FIX: remove nullable dates post upgrade to Rails 4

app/models/github_user_info.rb

@@ -10,8 +10,8 @@ end
 #  user_id        :integer          not null
 #  screen_name    :string(255)      not null
 #  github_user_id :integer          not null
-#  created_at     :datetime
-#  updated_at     :datetime
+#  created_at     :datetime         not null
+#  updated_at     :datetime         not null
 #
 # Indexes
 #