npm: bump sassdoc from 1.10.12 to 2.7.4

Bumps [sassdoc](https://github.com/SassDoc/sassdoc) from 1.10.12 to 2.7.4.
- [Release notes](https://github.com/SassDoc/sassdoc/releases)
- [Changelog](https://github.com/SassDoc/sassdoc/blob/master/CHANGELOG.md)
- [Commits](https://github.com/SassDoc/sassdoc/commits/2.7.4)

---
updated-dependencies:
- dependency-name: sassdoc
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>