Bump jinja2 from 2.11.1 to 2.11.3 in /docs (#706)

Bumps [jinja2](https://github.com/pallets/jinja) from 2.11.1 to 2.11.3.
- [Release notes](https://github.com/pallets/jinja/releases)
- [Changelog](https://github.com/pallets/jinja/blob/master/CHANGES.rst)
- [Commits](https://github.com/pallets/jinja/compare/2.11.1...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

@@ -1,6 +1,6 @@
 click==7.1.1
 future==0.18.2
-Jinja2==2.11.1
+Jinja2==2.11.3
 joblib==0.14.1
 livereload==2.6.1
 lunr==0.5.6