Add missing argument in CustomLog example.

Submitted by: Thomas =?iso-8859-1?q?Sj=F6gren?= <thomas@northernsecurity.net>
Reviewed by: Joshua Slive


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@96015 13f79535-47bb-0310-9956-ffa450edef68