Bump jinja2 from 2.10.1 to 2.11.3 in /docs

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](pallets/jinja@2.10.1...2.11.3)

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

Author: dependabot[bot]

docs/requirements.txt

@@ -1,7 +1,7 @@
 alabaster==0.7.7
 Babel==2.2.0
 docutils==0.12
-Jinja2==2.10.1
+Jinja2==2.11.3
 MarkupSafe==0.23
 Pygments==2.1
 pytz==2015.7