fetchTree(): Parse type attribute first
fetchTree(): Parse type attribute first

The 'url' attribute depends on whether type == 'git', so this is needed for

  builtins.fetchTree {url = "git@github.com:NixOS/nix.git"; type = "git";}

rycee/nix,NixOS/nix,NixOS/nix,NixOS/nix,rycee/nix,rycee/nix,NixOS/nix,rycee/nix,NixOS/nix,rycee/nix