marwaita-darkcyan: add update script

pkgs/by-name/ma/marwaita-darkcyan/package.nix

@@ -5,6 +5,7 @@
 , gtk-engine-murrine
 , gtk_engines
 , librsvg
+, gitUpdater
 }:
 
 stdenv.mkDerivation rec {
@@ -37,6 +38,8 @@ stdenv.mkDerivation rec {
     runHook postInstall
   '';
 
+  passthru.updateScript = gitUpdater { };
+
   meta = with lib; {
     description = "Manjaro Style of Marwaita GTK theme";
     homepage = "https://www.pling.com/p/1351213/";