[Snyk] Security upgrade html-proofer from 3.19.2 to 3.19.2

[snyk-bot]

Snyk has created this PR to fix one or more vulnerable packages in the `rubygems` dependencies of this project.

Changes included in this PR

• Changes to the following files to upgrade the vulnerable dependencies to a fixed version:
  • Gemfile
  • Gemfile.lock

Vulnerabilities that will be fixed

With an upgrade:

Severity	Priority Score (*)	Issue	Breaking Change	Exploit Maturity
	691/1000 Why? Recently disclosed, Has a fix available, CVSS 8.1	Use After Free SNYK-RUBY-NOKOGIRI-2413994	No	No Known Exploit

(*) Note that the real score may have changed since the PR was raised.

Check the changes in this PR to ensure they won't cause issues with your project.

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[FuhuXia]

done in https://github.com/GSA/data-strategy/pull/293