Bump jinja2 from 2.10.3 to 2.11.3 in /docs

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]

docs/requirements.txt

@@ -6,7 +6,7 @@ doc8==0.8.0
 docutils==0.15.2
 idna==2.8
 imagesize==1.1.0
-Jinja2==2.10.3
+Jinja2==2.11.3
 MarkupSafe==1.1.1
 packaging==19.2
 pbr==5.4.3