Bump urllib3 from 1.22 to 1.24.2

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.22 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@1.22...1.24.2)

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -23,6 +23,6 @@ snowballstemmer==1.2.1
 Sphinx==1.6.3
 sphinxcontrib-websupport==1.0.1
 tox==2.7.0
-urllib3==1.22
+urllib3==1.24.2
 virtualenv==15.1.0
 Werkzeug==0.12.2