fix migration version and updated old rails methods into rails migrations

db/migrate/20141104131625_generate_username.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class GenerateUsername < ActiveRecord::Migration
+class GenerateUsername < ActiveRecord::Migration[4.2]
   class TempUser < ActiveRecord::Base
     self.table_name = 'users'
   end
@@ -10,7 +10,7 @@ class GenerateUsername < ActiveRecord::Migration
       if user.username.blank?
         username = user.email.split('@')[0]
         username += user.id.to_s if TempUser.find_by(username: username)
-        user.update_attributes(username: username)
+        user.update(username: username)
       end
     end
   end