Minimal shell.nix with ruby package

shell.nix

let
        pkgs = import <nixpkgs> {};
        stdenv = pkgs.stdenv;
in
{
        developmentEnv = stdenv.mkDerivation rec {
                name = "developmentEnv";
                version = "nightly";
                src = ./.;
                buildInputs = [ 
                        pkgs.ruby18
                ];
        };
}