Bump django from 1.11.29 to 2.2.28 in /esp

Bumps [django](https://github.com/django/django) from 1.11.29 to 2.2.28.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@1.11.29...2.2.28)

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

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

Author: dependabot[bot]

esp/requirements.txt

@@ -1,5 +1,5 @@
 # Django
-Django==1.11.29
+Django==2.2.28
 
 # Django-specific packages
 git+https://github.com/learning-unlimited/[email protected] # Handles caching