fetchTarball {
  url = "https://github.com/NixOS/nixpkgs/archive/56b9f6fc8e1c3a4ad10ff7c61e461d7b7e038833.tar.gz";
  sha256 = "0v5y4wjfxbappsaibw88h7n1flcx7kpvg51mjv3h9m4aa3fn2c8q";
}

fetchTarball {
  url = "https://github.com/NixOS/nixpkgs/archive/c1427bf45ffd9f738cb811f980a7a4accf342783.tar.gz";
  sha256 = "16xmd9zlbiyqd90y5a2jqwvkmbn95wcxqk0qnxlf2lkryg8cvc89";
}

Upgrade to latest commit in nixos-18.09 channel
Upgrade to latest commit in nixos-18.09 channel
