use an old hugo version via nix flakes

flake.nix

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    old-hugo-nixpkgs.url = "github:NixOS/nixpkgs/4fe31ab170bbbdd089b05b268b681542886eb642";
    flake-utils.url = "github:numtide/flake-utils";
  };
  outputs = { self, nixpkgs, old-hugo-nixpkgs, flake-utils, }:
    flake-utils.lib.eachDefaultSystem
      (system:
        let
          pkgs = import nixpkgs { inherit system; };
          hugo = old-hugo-nixpkgs.legacyPackages.${system}.hugo;
        in
        with pkgs;
        {
          devShells.default = mkShell {
            buildInputs = [ hugo ];
          };
        }
      );
}