pythonPackages.django_modelcluster: disable for Python older than 3.5

pkgs/development/python-modules/django_modelcluster/default.nix

@@ -2,6 +2,7 @@
 , buildPythonPackage
 , fetchPypi
 , pytz
+, pythonOlder
 , six
 }:
 
@@ -14,6 +15,8 @@ buildPythonPackage rec {
     sha256 = "0zcn1b0lp9dg6xvz8p8v1hrrgqj71izqalqz2dp1nz5rbj3s34x2";
   };
 
+  disabled = pythonOlder "3.5";
+
   doCheck = false;
 
   propagatedBuildInputs = [ pytz six ];