Add redis to the requirements

requirements.txt

@@ -31,6 +31,7 @@ django_select2==6.0.1
 dj-database-url==0.5.0
 django-basic-auth-ip-whitelist==0.2.1
 django-heroku==0.3.1
+django-redis==4.9.0
 whitenoise==4.0
 gunicorn==19.9.0
 ConcurrentLogHandler==0.9.1