Manual experimental flags
Fixes:
Fix parsing of nix output when single paths are fetched.
Breaking changes:
For nix versions bigger than 2.3.x you need to manually enable at least
experimental-features = nix-command
in your /etc/nix/nix.conf
or
$HOME/.config/nix/nix.conf
or pass -build-flags "--experimental-features nix-command"
to nix-build-uncached
.