Update NotificationTransformer

app/Transformer/Api/Mastodon/v1/NotificationTransformer.php

@@ -20,7 +20,7 @@ class NotificationTransformer extends Fractal\TransformerAbstract
 		return [
 			'id'       		=> (string) $notification->id,
 			'type'       	=> $this->replaceTypeVerb($notification->action),
-			'created_at' 	=> (string) $notification->created_at->format('c'),
+			'created_at' 	=> (string) $notification->created_at->toIso8601ZuluString(),
 		];
 	}