nixos/collectd: Fix package option

Commit ed979124cad7596de539188e86664b3784c363ca was missing some code.

Changed files
+1 -1
nixos
modules
services
monitoring
+1 -1
nixos/modules/services/monitoring/collectd.nix
···
wantedBy = [ "multi-user.target" ];
serviceConfig = {
-
ExecStart = "${pkgs.collectd}/sbin/collectd -C ${conf} -P ${cfg.pidFile}";
+
ExecStart = "${cfg.package}/sbin/collectd -C ${conf} -P ${cfg.pidFile}";
Type = "forking";
PIDFile = cfg.pidFile;
User = optional (cfg.user!="root") cfg.user;