Issue description

Ditto.

Steps to reproduce

1. Build python2.buildEnv.override { extraLibs = with python2.pkgs; [ notebook ]; }; (you'll need ignoreCollisions; maybe that's the problem but it doesn't seem so);
2. Run jupyter-notebook;
3. Try to create new notebook; see that there are no kernels available.

Technical details

• Nixpkgs version: (run nix-instantiate --eval '<nixpkgs>' -A lib.nixpkgsVersion) c05ac3e