Bump urllib3 from 1.24.2 to 1.25

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.24.2 to 1.25.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/master/CHANGES.rst)
- [Commits](urllib3/urllib3@1.24.2...1.25)

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

requirements.txt

@@ -29,7 +29,7 @@ six==1.12.0
 transaction==2.4.0
 translationstring==1.3
 ujson==1.35
-urllib3==1.24.2
+urllib3==1.25
 venusian==1.2.0
 waitress==1.2.1
 WebOb==1.8.5