Bump graphene-django from 2.8.0 to 2.8.1 in /src/requirements

Bumps [graphene-django](https://github.com/graphql-python/graphene-django) from 2.8.0 to 2.8.1.
- [Release notes](https://github.com/graphql-python/graphene-django/releases)
- [Commits](https://github.com/graphql-python/graphene-django/compare/v2.8.0...v2.8.1)

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

src/requirements/production.txt

@@ -14,7 +14,7 @@ django-filter==2.2.0
 django-reversion==3.0.5
 django-wkhtmltopdf==3.3.0
 future==0.18.2
-graphene-django==2.8.0
+graphene-django==2.8.1
 html5lib==1.0.1
 icalendar==4.0.4
 ipython==7.12.0