[#612] Fix call to django.contirb.auth.views.password_reset_confirm()

One of the kwarg names for password_reset_confirm() has changed from
uidb36 to uidb64 causing the pwd reset confirmation to break.
Fix by calling with the correct kwarg.
Merge pull request #614 from akvo/feature/612_fixes_to_2.3.8

Feature/612 fixes to 2.3.8
[#612] Update requirements to get at fix in django-registration
Merge pull request #615 from akvo/feature/612_fixes_to_2.3.8

[#612] Update requirements to get at fix in django-registration
Merge pull request #616 from akvo/feature/django-upgrade

Feature/django upgrade