Remove Rails 5 deprecation warning.

db/migrate/20140925173220_create_user_fields.rb

@@ -3,7 +3,7 @@ class CreateUserFields < ActiveRecord::Migration
     create_table :user_fields do |t|
       t.string :name, null: false
       t.string :field_type, null: false
-      t.timestamps
+      t.timestamps null: false
     end
   end
 end