Bump html-proofer from 3.17.4 to 3.18.0

Bumps html-proofer from 3.17.4 to 3.18.0.

Commits

• fff1bd8 3.18.0
• a7f6ccd Merge pull request #609 from gjtorikian/calmer-error
• fea77d0 Capture errors
• 5a4afd2 Install deps first
• 49ad675 Lint
• 29d316d Never needed to raise
• See full diff in compare view