Bump django from 2.2.18 to 2.2.20

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] <[email protected]>

Author: dependabot[bot]

requirements_dev.txt

@@ -6,7 +6,7 @@ falcon==2.0.0; python_version<"3.0"
 falcon==3.0.0; python_version>="3.0"
 flask
 django==1.11.29; python_version<"3.0"
-django==2.2.18; python_version>="3.0"
+django==2.2.20; python_version>="3.0"
 djangorestframework==3.9.4
 requests==2.22.0
 responses==0.10.12