aleo-fonts: fix missing webfont output

pkgs/by-name/al/aleo-fonts/package.nix

@@ -16,8 +16,15 @@ stdenvNoCC.mkDerivation {
     hash = "sha256-HSxP5/sLHQTujBVt1u93625EXEc42lxpt8W1//6ngWM=";
   };
 
+  outputs = [
+    "out"
+    "webfont"
+  ];
+
   nativeBuildInputs = [ installFonts ];
 
+  preInstall = "rm -r fonts/old";
+
   meta = {
     description = "Slab serif typeface designed by Alessio Laiso";
     homepage = "https://github.com/AlessioLaiso/aleo";