Support Django 2.2 and 3.0

cas_server/models.py

@@ -15,9 +15,13 @@ from .default_settings import settings, SessionStore
 from django.db import models
 from django.db.models import Q
 from django.contrib import messages
-from django.utils.translation import ugettext_lazy as _
 from django.utils import timezone
-from django.utils.encoding import python_2_unicode_compatible
+try:
+    from django.utils.encoding import python_2_unicode_compatible
+    from django.utils.translation import ugettext_lazy as _
+except ImportError:
+    def python_2_unicode_compatible(f): return f
+    from django.utils.translation import gettext_lazy as _
 from django.core.mail import send_mail
 
 import re