bug#36074: Still got the issue in Xubuntu 18.4

[Andréas Livet]

Hello,

I'm running guix under Xubuntu 18.04 and still got the issue after 
modifying `/etc/systemd/system/guix-daemon.service` as stated in the patch.

After that I've done :

`systemctl restart guix-daemon`

`systemctl daemon-reload `

Should I done something else ?

I'm new to guix so sorry if it seems obvious.

Andréas