Changed migration helper back to using TableDefinition class instead of Table class.

Author: JohnColvin

lib/userstamp/migration_helper.rb

@@ -16,4 +16,4 @@ def userstamps(include_deleted_by = false)
   end
 end
 
-ActiveRecord::ConnectionAdapters::Table.send(:include, Ddb::Userstamp::MigrationHelper)
+ActiveRecord::ConnectionAdapters::TableDefinition.send(:include, Ddb::Userstamp::MigrationHelper)