Bump urllib3 from 1.25.7 to 1.25.8

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.25.7 to 1.25.8.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/master/CHANGES.rst)
- [Commits](urllib3/urllib3@1.25.7...1.25.8)

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

requirements.txt

@@ -33,7 +33,7 @@ six==1.14.0
 transaction==3.0.0
 translationstring==1.3
 ujson==1.35
-urllib3==1.25.7
+urllib3==1.25.8
 venusian==3.0.0
 waitress==1.4.2
 WebOb==1.8.5