Add comma for last item

Because the following `$model->save()` argument has trailing comma

Author: kenjis

user_guide_src/source/tutorial/create_news_items.rst

@@ -51,7 +51,7 @@ validation <../libraries/validation>` library to do this.
 
         if ($this->request->getMethod() === 'post' && $this->validate([
                 'title' => 'required|min_length[3]|max_length[255]',
-                'body'  => 'required'
+                'body'  => 'required',
             ]))
         {
             $model->save([