grandorgue: Use wrapGAppsHook3 to provide correct environment

That hook solves at least one problem when running GrandOrgue outside a
GTK desktop. That's related to GSettings directory not being configured.

Fixes NixOs/nixpkgs#397674

pkgs/by-name/gr/grandorgue/package.nix

@@ -2,6 +2,7 @@
   lib,
   stdenv,
   fetchFromGitHub,
+  wrapGAppsHook3,
   cmake,
   pkg-config,
   fftwFloat,
@@ -39,6 +40,7 @@ stdenv.mkDerivation rec {
     imagemagick
     libicns
     makeWrapper
+    wrapGAppsHook3
   ];
 
   buildInputs =