Bump gulp from 4.0.2 to 5.0.0 in /docs-tools

Bumps [gulp](https://github.com/gulpjs/gulp) from 4.0.2 to 5.0.0.
- [Release notes](https://github.com/gulpjs/gulp/releases)
- [Changelog](https://github.com/gulpjs/gulp/blob/master/CHANGELOG.md)
- [Commits](gulpjs/gulp@v4.0.2...v5.0.0)

---
updated-dependencies:
- dependency-name: gulp
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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