Bump @types/jest from 26.0.20 to 26.0.21 (#114)

Bumps [@types/jest](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/jest) from 26.0.20 to 26.0.21.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/jest)

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