Bump shelljs from 0.8.5 to 0.9.1

Bumps [shelljs](https://github.com/shelljs/shelljs) from 0.8.5 to 0.9.1.
- [Release notes](https://github.com/shelljs/shelljs/releases)
- [Changelog](https://github.com/shelljs/shelljs/blob/master/CHANGELOG.md)
- [Commits](shelljs/shelljs@v0.8.5...v0.9.1)

---
updated-dependencies:
- dependency-name: shelljs
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]