Bump html-proofer from 3.17.3 to 3.17.4

Bumps html-proofer from 3.17.3 to 3.17.4.

Commits

• e09f6be 💎 bump to 3.17.4
• a830821 Merge pull request #605 from gjtorikian/cache-crash
• ef4eafa Correct internal links when pulled from outdated cache
• See full diff in compare view