Fix missing/incorrect Model specifications in migrations

We need to define the required models within the migration (not below) to work reliably.

db/migrate/20140826073318_sorcery_core.rb

@@ -1,6 +1,9 @@
 # frozen_string_literal: true
 
 class SorceryCore < ActiveRecord::Migration[4.2]
+  class InternalUser < ApplicationRecord
+  end
+
   def change
     InternalUser.delete_all
     add_column :internal_users, :crypted_password, :string, null: false