[Snyk] Security upgrade jekyll from 3.8.5 to 3.9.0

[JohnHammond]

This PR was automatically created by Snyk using the credentials of a real user.

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
	589/1000 Why? Has a fix available, CVSS 7.5	Regular Expression Denial of Service (ReDoS) SNYK-RUBY-ADDRESSABLE-1316242	No	No Known Exploit
	505/1000 Why? Has a fix available, CVSS 5.6	Deserialization of Untrusted Data SNYK-RUBY-KRAMDOWN-1087436	No	No Known Exploit
	574/1000 Why? Has a fix available, CVSS 7.2	Remote Code Execution SNYK-RUBY-KRAMDOWN-585939	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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Learn how to fix vulnerabilities with free interactive lessons:

🦉 Regular Expression Denial of Service (ReDoS) 🦉 Deserialization of Untrusted Data 🦉 Remote Code Execution