xnec2c: provide update script

pkgs/by-name/xn/xnec2c/package.nix

@@ -9,6 +9,7 @@
   gtk3,
   blas,
   lapack,
+  nix-update-script,
 }:
 
 assert (!blas.isILP64) && (!lapack.isILP64);
@@ -36,6 +37,8 @@ stdenv.mkDerivation (finalAttrs: {
     lapack
   ];
 
+  passthru.updateScript = nix-update-script { };
+
   meta = {
     homepage = "https://www.xnec2c.org/";
     description = "Graphical antenna simulation";