Helix: switch to new format

hm_modules/helix.nix

@@ -12,7 +12,7 @@
   programs.helix = {
     enable = true;
     package = pkgs.unstable_pkgs.helix;
-    languages = [{
+    languages.language = [{
       name = "nix";
       formatter = { command = "nixpkgs-fmt"; };
       # config = { nil = { formatting = { command = "nixpkgs-fmt"; }; }; };