Merge pull request #9059 from totoprayogo1916/patch-2

docs: `referrer` is undefined

Author: kenjis

user_guide_src/source/libraries/user_agent/005.php

@@ -1,5 +1,5 @@
 <?php
 
 if ($agent->isReferral()) {
-    echo $agent->referrer();
+    echo $agent->getReferrer();
 }