update-luarocks-packages: use the current nixpkgs

restore the behavior of the previous updater that was using the current revision of nixpkgs instead of an outer one

maintainers/scripts/update-luarocks-packages

@@ -1,5 +1,6 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -p nix-prefetch-git luarocks-nix python3 python3Packages.GitPython nix -i python3
+#!nix-shell update-luarocks-shell.nix -i python3
+
 
 # format:
 # $ nix run nixpkgs.python3Packages.black -c black update.py

maintainers/scripts/update-luarocks-shell.nix

@@ -1,12 +1,13 @@
 { nixpkgs ? import ../.. { }
 }:
 with nixpkgs;
+let
+  pyEnv = python3.withPackages(ps: [ ps.GitPython ]);
+in
 mkShell {
   packages = [
-    bash
+    pyEnv
     luarocks-nix
     nix-prefetch-scripts
-    parallel
   ];
-  LUAROCKS_NIXPKGS_PATH = toString nixpkgs.path;
 }