Bump sinon from 4.1.5 to 4.2.0

Bumps [sinon](https://github.com/sinonjs/sinon) from 4.1.5 to 4.2.0.
- [Changelog](https://github.com/sinonjs/sinon/blob/master/docs/changelog.md)
- [Commits](https://github.com/sinonjs/sinon/compare/v4.1.5...v4.2.0)