Bump mocha from 8.2.1 to 8.4.0 (#243)

Bumps [mocha](https://github.com/mochajs/mocha) from 8.2.1 to 8.4.0.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/master/CHANGELOG.md)
- [Commits](mochajs/mocha@v8.2.1...v8.4.0)

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