[arch-mirrors] If your are syncing of UK2, switch to LeaseWeb

Hello, Our uk2 mirror has had some problems recently, and unfortunately they haven't been resolved yet[1]. Therefore we recommend that all tier 2 mirrors that sync off the uk2 mirror switch to our LeaseWeb mirror. Feel free to switch back to UK2, when the problems are resolved. [1]I've been told they're working on it though. Best regards, Jakob