flex-ndax: provide update script

pkgs/by-name/fl/flex-ndax/package.nix

@@ -4,6 +4,7 @@
   buildGoModule,
   fetchFromGitHub,
   libpulseaudio,
+  nix-update-script,
 }:
 
 buildGoModule rec {
@@ -21,6 +22,8 @@ buildGoModule rec {
 
   vendorHash = "sha256-05LWJm4MoJqjJaFrBZvutKlqSTGl4dSp433AfHHO6LU=";
 
+  passthru.updateScript = nix-update-script { };
+
   meta = {
     broken = stdenv.hostPlatform.isDarwin;
     homepage = "https://github.com/kc2g-flex-tools/nDAX";