chore(deps): bump django from 2.2.18 to 2.2.20 in /rootfs

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]

rootfs/requirements.txt

@@ -1,6 +1,6 @@
 # Drycc controller requirements
 backoff==1.10.0
-django==2.2.18
+django==2.2.20
 django-auth-ldap==2.2.0
 django-cors-middleware==1.5.0
 django-guardian==2.3.0