[Snyk] Security upgrade just-the-docs from 0.3.3 to 0.4.0

[Semsemq]

Snyk has created this PR to fix 1 vulnerabilities in the rubygems dependencies of this project.

Snyk changed the following file(s):

• docs/Gemfile.lock

Vulnerabilities that will be fixed with an upgrade:

	Issue	Score
	Regular Expression Denial of Service (ReDoS) SNYK-RUBY-REXML-13110060	50

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Learn how to fix vulnerabilities with free interactive lessons:

🦉 Regular Expression Denial of Service (ReDoS)