Bump urllib3 from 1.25.3 to 1.25.8

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.25.3 to 1.25.8.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.25.3...1.25.8)

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

requirements.txt

@@ -28,5 +28,5 @@ torch==1.2.0
 torchtext==0.4.0
 torchvision==0.4.0a0+9232c4a
 tqdm==4.30.0
-urllib3==1.25.3
+urllib3==1.25.8
 Werkzeug==0.15.4