Bump django from 2.2.10 to 2.2.13 in /app

Bumps [django](https://github.com/django/django) from 2.2.10 to 2.2.13.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/2.2.10...2.2.13)

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

app/requirements.txt

@@ -4,7 +4,7 @@ colour==0.1.5
 chardet==3.0.4
 coverage==4.5.3
 dj-database-url==0.5.0
-Django==2.2.10
+Django==2.2.13
 django-cloud-browser==0.5.0
 django-cors-headers==3.1.1
 django-filter==2.0.0