ivpn{,-service}: add nix-update-script

pkgs/tools/networking/ivpn/default.nix

@@ -12,6 +12,7 @@
   iptables,
   gawk,
   util-linux,
+  nix-update-script,
 }:
 
 builtins.mapAttrs
@@ -47,6 +48,8 @@ builtins.mapAttrs
           mv $out/bin/{${attrs.modRoot},${pname}}
         '';
 
+        passthru.updateScript = nix-update-script { };
+
         meta = {
           description = "Official IVPN Desktop app";
           homepage = "https://www.ivpn.net/apps";