Remove django cas server in CI dependencies

corres2math/settings.py

@@ -51,7 +51,6 @@ INSTALLED_APPS = [
     'django.forms',
 
     'bootstrap_datepicker_plus',
-    'cas_server',
     'crispy_forms',
     'django_tables2',
     'haystack',
@@ -68,6 +67,7 @@ INSTALLED_APPS = [
 
 if "test" not in sys.argv:  # pragma: no cover
     INSTALLED_APPS += [
+        'cas_server',
         'django_extensions',
         'mailer',
     ]