chore(deps): bump jinja2 from 2.10.3 to 2.11.3 in /backend

Bumps [jinja2](https://github.com/pallets/jinja) from 2.10.3 to 2.11.3.
- [Release notes](https://github.com/pallets/jinja/releases)
- [Changelog](https://github.com/pallets/jinja/blob/master/CHANGES.rst)
- [Commits](pallets/jinja@2.10.3...2.11.3)

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

Author: dependabot[bot]

backend/requirements.txt

@@ -15,7 +15,7 @@ future==0.18.2
 gunicorn==20.0.4
 importlib-metadata==1.3.0
 itsdangerous==1.1.0
-Jinja2==2.10.3
+Jinja2==2.11.3
 Mako==1.1.0
 MarkupSafe==1.1.1
 marshmallow==3.3.0