build(deps): bump requests from 2.19.1 to 2.20.0

Bumps [requests](https://github.com/requests/requests) from 2.19.1 to 2.20.0.
- [Release notes](https://github.com/requests/requests/releases)
- [Changelog](https://github.com/kennethreitz/requests/blob/master/HISTORY.md)
- [Commits](psf/requests@v2.19.1...v2.20.0)

Author: dependabot[bot]