nixos/services.nginx: Fix globalRedirect example

Virtual host globalRedirect attribute accepts a hostname not a URL

https://github.com/NixOS/nixpkgs/blob/09a9a472ee783b40c2a3dd287bbe9d3c60f8fc58/nixos/modules/services/web-servers/nginx/default.nix#L167

nixos/modules/services/web-servers/nginx/vhost-options.nix

@@ -142,10 +142,10 @@ with lib;
     globalRedirect = mkOption {
       type = types.nullOr types.str;
       default = null;
-      example = http://newserver.example.org/;
+      example = "newserver.example.org";
       description = ''
         If set, all requests for this host are redirected permanently to
-        the given URL.
+        the given hostname.
       '';
     };