build(deps): bump @types/jest from 26.0.15 to 26.0.20 in /lib (wtho#54)

Bumps [@types/jest](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/jest) from 26.0.15 to 26.0.20.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/jest)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]