mate: add passthru update script

pkgs/desktops/mate/mate-session-manager/default.nix

@@ -1,6 +1,6 @@
 { lib, stdenv, fetchurl, pkg-config, gettext, xtrans, dbus-glib, systemd,
   libSM, libXtst, gtk3, epoxy, polkit, hicolor-icon-theme, mate,
-  wrapGAppsHook, fetchpatch
+  wrapGAppsHook, fetchpatch, mateUpdateScript
 }:
 
 stdenv.mkDerivation rec {
@@ -49,6 +49,8 @@ stdenv.mkDerivation rec {
 
   passthru.providedSessions = [ "mate" ];
 
+  passthru.updateScript = mateUpdateScript { inherit pname version; };
+
   meta = with lib; {
     description = "MATE Desktop session manager";
     homepage = "https://github.com/mate-desktop/mate-session-manager";