Bump urllib3 from 1.21.1 to 1.24.2

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.21.1 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@1.21.1...1.24.2)

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

Author: dependabot[bot]

requirements.txt

@@ -7,4 +7,4 @@ grequests==0.3.0
 idna==2.5
 requests==2.18.1
 terminaltables==3.1.0
-urllib3==1.21.1
+urllib3==1.24.2