py38: Django 2.1 (#27555)

requirements-base.txt

@@ -10,7 +10,7 @@ dataclasses==0.8; python_version <= '3.6'
 datadog==0.29.3
 django-crispy-forms==1.7.2
 django-picklefield==1.0.0
-Django==2.0.13
+Django==2.1.15
 djangorestframework==3.11.2
 email-reply-parser==0.5.12
 google-api-core==1.25.1