Fix cert updating script

The mirrors ran into this problem:

  Subject: Cron <root@cdn3> test -e /usr/sbin/libravatar-update-certs && /usr/sbin/libravatar-update-certs (failed)

  Libravatar SSL certificate updated. Restarting Apache...

  /usr/sbin/libravatar-update-certs: 34: apache2ctl: not found