Bump s3transfer from 0.2.1 to 0.3.0 (from PR #1927)
Bump s3transfer from 0.2.1 to 0.3.0 (from PR #1927)

Bumps [s3transfer](https://github.com/boto/s3transfer) from 0.2.1 to 0.3.0.
- [Release notes](https://github.com/boto/s3transfer/releases)
- [Changelog](https://github.com/boto/s3transfer/blob/develop/CHANGELOG.rst)
- [Commits](https://github.com/boto/s3transfer/compare/0.2.1...0.3.0)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>

mozilla-services/tecken,mozilla-services/tecken,mozilla-services/tecken,mozilla-services/tecken