etebase-server: mark no longer broken on darwin

pkgs/servers/etebase/default.nix

···
     description = "An Etebase (EteSync 2.0) server so you can run your own.";
     license = licenses.agpl3Only;
     maintainers = with maintainers; [ felschr ];
-    broken = stdenv.isDarwin;
   };
 }