Update django requirement from <3.0,>=2.2.0 to >=2.2.0,<4.0

Updates the requirements on [django](https://github.com/django/django) to permit the latest version.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.2...3.0.3)

Signed-off-by: dependabot-preview[bot] <[email protected]>

requirements.txt

@@ -1,4 +1,4 @@
-django>=2.2.0,<3.0
+django>=2.2.0,<4.0
 idna>=2.5,<2.10
 requests>=2.13.0
 Markdown==3.2.1