Support Django 2.2 and 3.0

cas_server/default_settings.py

@@ -12,10 +12,15 @@
 """Default values for the app's settings"""
 from django.conf import settings
 from django.templatetags.static import static
-from django.utils.translation import ugettext_lazy as _
 
 from importlib import import_module
 
+import sys
+if sys.version_info < (3, ):
+    from django.utils.translation import ugettext_lazy as _
+else:
+    from django.utils.translation import gettext_lazy as _
+
 
 try:
     #: URL to the logo showed in the up left corner on the default templates.