[Snyk] Fix for 3 vulnerabilities

[snyk-bot]

Key changes are:

• Upgrade various libraries to be compliant (specifically nokogiri)
• Upgrade html-proofer
• Add escape functionality for html items that were not being escaped properly and causing html-proofer to fail

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

⚠️ Warning

``` Failed to update the Gemfile.lock, please update manually before merging. ```

Vulnerabilities that will be fixed

With an upgrade:

Severity	Issue	Breaking Change	Exploit Maturity
	Remote Code Execution SNYK-RUBY-KRAMDOWN-585939	Yes	No Known Exploit
	Uncontrolled Memory Allocation SNYK-RUBY-NOKOGIRI-534637	No	No Known Exploit
	Denial of Service (DoS) SNYK-RUBY-NOKOGIRI-552159	No	No Known Exploit

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

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[jbrown-xentity]

Related to SDG Remediations