Add "su" directive on logrotate's config

To make sure it will use the default user and group and prevent errors if the parent directory is world writable.
See http://stackoverflow.com/questions/26482773/apache-and-logrotate-configuration

config/logrotate/mconf-web

@@ -7,4 +7,5 @@
   compress
   copytruncate
   notifempty
+  su mconf www-data
 }