Add zlib-devel to the BuildReq in the RPM Spec file, which allows mod_deflate to be built.

PR: 37968
Noticed By: Loïc Mahé <loic.mahe regis-dgac.net>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@415945 13f79535-47bb-0310-9956-ffa450edef68