backport r893874 from trunk

Fix the ProxyPass example according to the trailing slash rule.

Submitted by: inoue <inoue ariel-networks.com>
PR: 48444

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@893875 13f79535-47bb-0310-9956-ffa450edef68