Bump urllib3 from 1.26.3 to 1.26.4

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.3 to 1.26.4.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/1.26.4/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.3...1.26.4)

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

requirements.txt

@@ -11,5 +11,5 @@ requests-toolbelt==0.9.1
 six==1.15.0
 tqdm==4.59.0
 twine==3.3.0
-urllib3==1.26.3
+urllib3==1.26.4
 webencodings==0.5.1