nixos/node-red: fix cfg.package default value

This fixes the following eval error:

```
error: nodePackages.node-red cannot be found in pkgs
```

when having `services.node-red.enable = true;` without specifying
`services.node-red.package`, just like the nixos VM test.

Follow-up of f509382c11, which attempted
to fix this as well.

Breakage introduced in 0a37316d6c.

nixos/modules/services/web-apps/node-red.nix

@@ -19,7 +19,7 @@ in
   options.services.node-red = {
     enable = mkEnableOption (lib.mdDoc "the Node-RED service");
 
-    package = mkPackageOption pkgs "nodePackages.node-red" { };
+    package = mkPackageOption pkgs.nodePackages "node-red" { };
 
     openFirewall = mkOption {
       type = types.bool;