Support SCP-like URLs in builtins.fetchGit attrs
Support SCP-like URLs in builtins.fetchGit attrs

This extends https://github.com/NixOS/nix/pull/4978 with
supporting the SCP-like urls in expressions like

```nix
builtins.fetchGit {
  url = "git@github.com:NixOS/nix.git";
  ref = "master";
}
```

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