Bump jinja2 from 2.8 to 2.11.3

Bumps [jinja2](https://github.com/pallets/jinja) from 2.8 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@2.8...2.11.3)

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

requirements.txt

@@ -22,7 +22,7 @@ gunicorn==18.0
 httmock==1.2.2
 iso8601==0.1.10
 itsdangerous==0.24
-Jinja2==2.8
+Jinja2==2.11.3
 Mako==1.0.0
 MarkupSafe==0.23
 marrow.util==1.2.3