pkgs: pass nixpkgs config properly

see cee4094d91
for details of upstream changes

nix/sources.json

@@ -32,7 +32,7 @@
     "nix-hexchen": {
         "ref": "main",
         "repo": "https://gitlab.com/hexchen/nixfiles.git",
-        "rev": "ea33a93da0bac59b757e7a059028526f47c2b852",
+        "rev": "5369d696f5381bf410408224fd8fa68480a96ff1",
         "type": "git"
     },
     "nixos-mailserver": {

pkgs/default.nix

@@ -1,8 +1,8 @@
-{ ... }:
+{ config ? {}, system ? builtins.currentSystem, ... }@args:
 
 let
   sources = import ../nix/sources.nix;
-  pkgs = import sources.nixpkgs { config = { allowUnfree = true; }; };
+  pkgs = import sources.nixpkgs args;
 
   callPackage = pkgs.lib.callPackageWith (pkgs // newpkgs);