Downgrade versions of django and django-filter (django-filter not working with django 2.1)

requirements.txt

 aiosmtpd                    # debian: python3-aiosmtpd
 bleach                      # debian: python3-bleach
-django                      # debian: python3-django
+django<2.1                  # debian: python3-django
 django-allauth              # debian (buster): python3-django-allauth
 django-crispy-forms         # debian: python3-django-crispy-forms
-django-filter               # debian: python3-django-filters
+django-filter<2             # debian: python3-django-filters
 django-haystack             # debian: python3-django-haystack
 django-ical                 # NOT IN DEBIAN
 django-imagekit             # debian (buster): python3-django-imagekit