[Snyk] Security upgrade jekyll from 3.7.2 to 4.0.0

[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:
  • src/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

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

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