Bump django from 3.1.6 to 3.1.13 (#259)

Bumps [django](https://github.com/django/django) from 3.1.6 to 3.1.13.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@3.1.6...3.1.13)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -9,7 +9,7 @@ click==7.1.2
 coverage==5.5
 defusedxml==0.6.0
 dj-database-url==0.5.0
-Django==3.1.6
+Django==3.1.13
 django-allauth==0.42.0
 django-heroku==0.3.1
 django-storages==1.10.1