fix update-python-libraries

maintainers/scripts/update-python-libraries

@@ -1,3 +1,5 @@
 #!/bin/sh
-exec nix-shell -p "python3.withPackages(ps: with ps; [ packaging requests toolz ])" -p git --run pkgs/development/interpreters/python/update-python-libraries/update-python-libraries.py
+build=`nix-build -E "with import (fetchTarball "channel:nixpkgs-unstable") {}; python3.withPackages(ps: with ps; [ packaging requests toolz ])"`
+python=${build}/bin/python
+exec ${python} pkgs/development/interpreters/python/update-python-libraries/update-python-libraries.py $@