Bump django from 2.1 to 2.1.11 in /problems/webdev/django_pn_tracker

Bumps [django](https://github.com/django/django) from 2.1 to 2.1.11.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.1...2.1.11)

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

Author: dependabot[bot]

problems/webdev/django_pn_tracker/requirements.txt

@@ -1 +1 @@
-django==2.1
+django==2.1.11