Bump jsonschema from 3.0.0b1 to 3.0.0b3
Bump jsonschema from 3.0.0b1 to 3.0.0b3

Bumps [jsonschema](https://github.com/Julian/jsonschema) from 3.0.0b1 to 3.0.0b3.
- [Release notes](https://github.com/Julian/jsonschema/releases)
- [Changelog](https://github.com/Julian/jsonschema/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/Julian/jsonschema/compare/v3.0.0b1...v3.0.0b3)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
Kinto/kinto-attachment