Bump urllib3 from 1.25.3 to 1.25.8 in /app

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](https://github.com/urllib3/urllib3/compare/1.25.3...1.25.8)

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

app/requirements.txt

@@ -34,7 +34,7 @@ python-memcached==1.59
 requests==2.22.0
 six==1.12.0
 terminaltables==3.1.0
-urllib3==1.25.3
+urllib3==1.25.8
 uWSGI==2.0.18
 visitor==0.1.3
 Werkzeug==0.15.5