ci was throwing errors as it couldn't parse apache config file format as xml. change xml parser to ApacheConf parser as defined/supported by pygments

Author: rouilj

doc/installation.txt

@@ -1134,7 +1134,7 @@ the following apache config to
 /etc/apache2/sites-available/roundup-foo (under debian/Ubunutu, modify
 as needed):
 
-  .. code:: xml
+  .. code:: ApacheConf
 
     ServerAdmin [email protected]
     ErrorLog /var/log/apache2/error.log