Update NotificationTransformer

app/Transformer/Api/NotificationTransformer.php

@@ -17,7 +17,7 @@ class NotificationTransformer extends Fractal\TransformerAbstract
 		return [
 			'id'       		=> (string) $notification->id,
 			'type'       	=> $this->replaceTypeVerb($notification->action),
-			'created_at' 	=> (string) $notification->created_at,
+			'created_at' 	=> (string) $notification->created_at->format('c'),
 			'account' 		=> null,
 			'status' 		=> null
 		];