steamPackages.steam: use hash instead of sha256 attr

  src = fetchurl {

    # use archive url so the tarball doesn't 404 on a new release

    url = "https://repo.steampowered.com/steam/archive/stable/steam_${finalAttrs.version}.tar.gz";

    sha256 = "sha256-sO07g3j1Qejato2LWJ2FrW3AzfMCcBz46HEw7aKxojQ=";

    hash = "sha256-sO07g3j1Qejato2LWJ2FrW3AzfMCcBz46HEw7aKxojQ=";

  };

  makeFlags = [ "DESTDIR=$(out)" "PREFIX=" ];