Bump django in /days/053-056-django-registration/demo

Bumps [django](https://github.com/django/django) from 2.2.18 to 2.2.20. - [Release notes](https://github.com/django/django/releases) - [Commits](django/django@2.2.18...2.2.20) Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

days/053-056-django-registration/demo/requirements.txt

@@ -1,2 +1,2 @@
-django==2.2.18
+django==2.2.20
 django-registration==3.1.2