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

@@ -12,4 +12,4 @@ pytest==3.5.0
 pytest-cov==2.5.1
 requests==2.18.4
 six==1.11.0
-urllib3==1.22
+urllib3==1.24.2