Bump cryptography from 2.6.1 to 2.7
Bump cryptography from 2.6.1 to 2.7

Bumps [cryptography](https://github.com/pyca/cryptography) from 2.6.1 to 2.7.
- [Release notes](https://github.com/pyca/cryptography/releases)
- [Changelog](https://github.com/pyca/cryptography/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pyca/cryptography/compare/2.6.1...2.7)
Kinto/kinto-dist,Kinto/kinto-dist,mozilla-services/kinto-dist,mozilla-services/kinto-dist