fix: bump django from 2.2.20 to 2.2.21 (#1533)

* build(deps): bump django from 2.2.20 to 2.2.21

Bumps [django](https://github.com/django/django) from 2.2.20 to 2.2.21.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.2.20...2.2.21)

---
updated-dependencies:
- dependency-name: django
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

setup.py

@@ -22,7 +22,7 @@
     package_dir={"aimmo": "aimmo"},
     include_package_data=True,
     install_requires=[
-        "django==2.2.20",
+        "django==2.2.21",
         "django-js-reverse==0.9.1",
         "djangorestframework==3.12.2",
         "eventlet==0.29.1",