Bump jinja2 from 2.10.1 to 2.11.3 in /docs (#224)

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>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/requirements.txt

@@ -6,7 +6,7 @@ alabaster==0.7.8
 Babel==2.3.4
 docutils==0.12
 imagesize==0.7.1
-Jinja2==2.10.1
+Jinja2==2.11.3
 MarkupSafe==0.23
 Pygments==2.1.3
 pytz==2016.4