Bump jinja2 from 2.6 to 2.11.3

Bumps [jinja2](https://github.com/pallets/jinja) from 2.6 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@2.6...2.11.3)

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

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 Flask==0.9
-Jinja2==2.6
+Jinja2==2.11.3
 Werkzeug==0.8.3
 argparse==1.2.1
 wsgiref==0.1.2