[Snyk] Fix for 1 vulnerabilities - Examples(Zoo App) - Rack 3.x

[mefellows]

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: - 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 :-------------------------:|-------------------------|:-------------------------|:-------------------------|:-------------------------  | **616/1000**
**Why?** Proof of Concept exploit, Has a fix available, CVSS 5.9 | Web Cache Poisoning
[SNYK-RUBY-RACK-1061917](https://snyk.io/vuln/SNYK-RUBY-RACK-1061917) | Yes | Proof of Concept (*) 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. ------------ **Note:** *You are seeing this because you or someone else with access to this repository has authorized Snyk to open fix PRs.* For more information: 🧐 [View latest project report](https://app.snyk.io/org/pact-foundation-808/project/b6444bbf-90d0-4f04-9fa5-50a7fa41d790?utm_source=github&utm_medium=referral&page=fix-pr) 🛠 [Adjust project settings](https://app.snyk.io/org/pact-foundation-808/project/b6444bbf-90d0-4f04-9fa5-50a7fa41d790?utm_source=github&utm_medium=referral&page=fix-pr/settings) 📚 [Read more about Snyk's upgrade and patch logic](https://support.snyk.io/hc/en-us/articles/360003891078-Snyk-patches-to-fix-vulnerabilities) [//]: # (snyk:metadata:{"prId":"44d4799e-7862-42b7-b15b-ec7590222454","prPublicId":"44d4799e-7862-42b7-b15b-ec7590222454","dependencies":[{"name":"pact","from":"1.62.0","to":"1.63.0"},{"name":"rack","from":"2.2.4","to":"3.0.0"}],"packageManager":"rubygems","projectPublicId":"b6444bbf-90d0-4f04-9fa5-50a7fa41d790","projectUrl":"https://app.snyk.io/org/pact-foundation-808/project/b6444bbf-90d0-4f04-9fa5-50a7fa41d790?utm_source=github&utm_medium=referral&page=fix-pr","type":"auto","patch":[],"vulns":["SNYK-RUBY-RACK-1061917"],"upgrade":["SNYK-RUBY-RACK-1061917"],"isBreakingChange":true,"env":"prod","prType":"fix","templateVariants":["pr-warning-shown","priorityScore"],"priorityScoreList":[616]}) --- **Learn how to fix vulnerabilities with free interactive lessons:** 🦉 [Learn about vulnerability in an interactive lesson of Snyk Learn.](https://learn.snyk.io/?loc=fix-pr)

[YOU54F]

Stopped from moving to Rack 3.x due to pin in pact-mock_service

Bundler could not find compatible versions for gem "rack":
  In Gemfile:
    rack (~> 3.0, >= 3.0.0)

    pact was resolved to 1.63.0, which depends on
      pact-mock_service (~> 3.0, >= 3.3.1) was resolved to 3.11.0, which depends on
        rack (~> 2.0)

[YOU54F]

Fixed in #308