[Snyk] Fix for 1 vulnerabilities

[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:
  • example/zoo-app/Gemfile

⚠️ Warning

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

Vulnerabilities that will be fixed

With an upgrade:

Severity	Priority Score (*)	Issue	Breaking Change	Exploit Maturity
	661/1000 Why? Recently disclosed, Has a fix available, CVSS 7.5	Denial of Service (DoS) SNYK-RUBY-RACK-3356639	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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🦉 Denial of Service (DoS)

[YOU54F]

closed by #294