mpd: Use package from unstable

The version from 20.09 logs every time a client connects (which pollutes
the journal) and I did not find an easy way to change this. The logging
was changed in a newer mpd version and the default log level now doesn’t
log connects.

users/simon/modules/mpd.nix

@@ -7,6 +7,7 @@ lib.mkIf nixosConfig.sbruder.gui.enable {
     enable = true;
     musicDirectory = "~/Music";
     network.listenAddress = "${config.services.mpd.dataDir}/socket";
+    package = pkgs.unstable.mpd;
     extraConfig = ''
       zeroconf_enabled   "no"