List Item Abbreviation

Can not update list item abbreviation because update() method is
expecting 'abbrev' key so this corrects the key.

include/ajax.forms.php

@@ -172,7 +172,7 @@ class DynamicFormsAjaxAPI extends AjaxController {
                 $item->update([
                     'name' =>   $basic['name'],
                     'value' =>  $basic['value'],
-                    'extra' =>  $basic['extra'],
+                    'abbrev' =>  $basic['extra'],
                 ]);
             }
         }