Bump urllib3 from 1.25.5 to 1.25.6

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.25.5 to 1.25.6.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/master/CHANGES.rst)
- [Commits](urllib3/urllib3@1.25.5...1.25.6)

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

requirements.txt

@@ -3,4 +3,4 @@ chardet==3.0.4
 idna==2.8
 requests==2.22.0
 Unidecode==1.1.1
-urllib3==1.25.5
+urllib3==1.25.6