Bump sinon from 6.3.3 to 6.3.4

Bumps [sinon](https://github.com/sinonjs/sinon) from 6.3.3 to 6.3.4.
- [Release notes](https://github.com/sinonjs/sinon/releases)
- [Changelog](https://github.com/sinonjs/sinon/blob/master/docs/changelog.md)
- [Commits](https://github.com/sinonjs/sinon/compare/v6.3.3...v6.3.4

)

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