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

fetchTarball {
  url = "https://github.com/NixOS/nixpkgs/archive/a7e559a5504572008567383c3dc8e142fa7a8633.tar.gz";
  sha256 = "16j95q58kkc69lfgpjkj76gw5sx8rcxwi3civm0mlfaxxyw9gzp6";
}

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