crystal = super.crystal.overrideAttrs(oldAttrs: rec {
  version = "0.31.1";
  src = fetchFromGitHub {
    owner  = "crystal-lang";
    repo   = "crystal";
    rev    = version;
    sha256 = "1dswxa32w16gnc6yjym12xj7ibg0g6zk3ngvl76lwdjqb1h6lwz8";
});