Update requests requirement from <2.21,>=2.4.2 to >=2.4.2,<2.22
Update requests requirement from <2.21,>=2.4.2 to >=2.4.2,<2.22

Updates the requirements on [requests](https://github.com/requests/requests) to permit the latest version.
- [Release notes](https://github.com/requests/requests/releases)
- [Changelog](https://github.com/requests/requests/blob/master/HISTORY.md)
- [Commits](https://github.com/requests/requests/commits/v2.21.0)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
zooniverse/panoptes-python-client