lxd: `pkg.lxd` does not point to the binaries

`pkg.lxd.bin` does

nixos/modules/virtualisation/lxd.nix

···
         # TODO(wkennington): Add lvm2 and thin-provisioning-tools
         path = with pkgs; [ acl rsync gnutar xz btrfs-progs ];
 
-        serviceConfig.ExecStart = "@${pkgs.lxd}/bin/lxd lxd --syslog --group lxd";
+        serviceConfig.ExecStart = "@${pkgs.lxd.bin}/bin/lxd lxd --syslog --group lxd";
         serviceConfig.Type = "simple";
         serviceConfig.KillMode = "process"; # when stopping, leave the containers alone
       };