Merge pull request #6526 from kenjis/fix-docs-Response-setLastModified

docs: fix inappropriate sample code in Response

Author: kenjis

user_guide_src/source/outgoing/response/022.php

@@ -1,4 +1,4 @@
 <?php
 
 $response->setLastModified(date('D, d M Y H:i:s'));
-$response->setLastModified(DateTime::createFromFormat('u', $time));
+$response->setLastModified(DateTime::createFromFormat('U', $timestamp));