Bump jinja2 from 2.10.1 to 2.11.3 in /app

Bumps [jinja2](https://github.com/pallets/jinja) from 2.10.1 to 2.11.3.
- [Release notes](https://github.com/pallets/jinja/releases)
- [Changelog](https://github.com/pallets/jinja/blob/master/CHANGES.rst)
- [Commits](https://github.com/pallets/jinja/compare/2.10.1...2.11.3)

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

app/requirements.txt

@@ -21,7 +21,7 @@ Flask-WTF==0.14.2
 greenlet==0.4.15
 idna==2.8
 itsdangerous==1.1.0
-Jinja2==2.10.1
+Jinja2==2.11.3
 lxml==4.4.1
 MarkupSafe==1.1.1
 marshmallow==3.0.0