Bump html-proofer from 3.18.5 to 3.18.6

Bumps [html-proofer](https://github.com/gjtorikian/html-proofer) from 3.18.5 to 3.18.6.
- [Release notes](https://github.com/gjtorikian/html-proofer/releases)
- [Commits](https://github.com/gjtorikian/html-proofer/compare/v3.18.5...v3.18.6)
8 jobs for dependabot/bundler/html-proofer-3.18.6 in 2 minutes and 48 seconds (queued for 1 second)