defualt.nix: unpin

let it fail in CI which is configured to build it at least
once a month so we know about any possible breakage.

Author: sorki

default.nix

@@ -1,14 +1,6 @@
-{ rev ?  "272fad732d39b24c4549c475176e0d8cbc8c897a"
-, pkgs ?
-    if ((rev == "") || (rev == "default") || (rev == "local"))
-      then import <nixpkgs> {}
-      # Do not guard with hash, so the project is able to use current channels (rolling `rev`) of Nixpkgs
-      else import (builtins.fetchTarball "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz") {}
-    // {
-      # Try to build dependencies even if they are marked broken.
-      config.allowBroken = true;
-    }
-}: let
+{ pkgs ? import <nixpkgs> {}
+}:
+let
   overlay = import ./overlay.nix pkgs pkgs.haskell.lib;
   overrideHaskellPackages = orig: {
     buildHaskellPackages =