Bump jinja2 from 2.10 to 2.11.3 in /docs (#667)

Bumps [jinja2](https://github.com/pallets/jinja) from 2.10 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...2.11.3)

Signed-off-by: dependabot[bot] <[email protected]>

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

Author: dependabot[bot]

docs/requirements.txt

@@ -6,7 +6,7 @@ chardet==3.0.4
 docutils==0.14
 idna==2.8
 imagesize==1.1.0
-Jinja2==2.10
+Jinja2==2.11.3
 livereload==2.6.0
 MarkupSafe==1.1.0
 packaging==18.0