Fix for missing + sign in preg_replace in _underscore call

Author: igorwulff

lib/internal/Magento/Framework/DataObject.php

@@ -454,7 +454,8 @@ protected function _underscore($name)
         $result = strtolower(
             trim(
                 preg_replace(
-                    '/([A-Z]|[0-9])/', "_$1",
+                    '/([A-Z]|[0-9]+)/', 
+                    "_$1",
                     lcfirst(
                         substr(
                             $name,