Bump urllib3 from 1.24.1 to 1.24.2 in /docs

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.24.1 to 1.24.2.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/master/CHANGES.rst)
- [Commits](urllib3/urllib3@1.24.1...1.24.2)

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

Author: dependabot[bot]

docs/requirements.txt

@@ -24,5 +24,5 @@ sphinx-autobuild==0.7.1
 sphinx-rtd-theme==0.4.2
 sphinxcontrib-websupport==1.1.0
 tornado==5.1.1
-urllib3==1.24.1
+urllib3==1.24.2
 watchdog==0.9.0