Bump html-proofer from 3.16.0 to 3.17.1

Bumps html-proofer from 3.16.0 to 3.17.1.

Commits

• 9a9552d 💎 bump to 3.17.1
• e5d4fb5 Merge pull request #594 from gjtorikian/root-folder-update
• a016f01 drop the regex
• 26c97fa Rubocop
• fb71f78 Let root_dir work for directories
• ffb6bd9 Corrections to root_dir docs
• 5badc4e 💎 bump to 3.17.0
• 5969f09 Merge pull request #592 from gjtorikian/rubocop
• 9052b65 minor fixes
• 0c20549 lint
• Additional commits viewable in compare view