[Security] Bump requests from 2.15.1 to 2.20.0

Bumps [requests](https://github.com/psf/requests) from 2.15.1 to 2.20.0. **This update includes a security fix.**
- [Release notes](https://github.com/psf/requests/releases)
- [Changelog](https://github.com/psf/requests/blob/master/HISTORY.md)
- [Commits](psf/requests@v2.15.1...v2.20.0)

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