[Snyk] Security upgrade express from 4.16.4 to 4.21.1#250

<h3>Snyk has created this PR to fix one or more vulnerable packages in the `yarn` dependencies of this project.</h3> #### Changes included in this PR - Changes to the following files to upgrade the vulnerable dependencies to a fixed version: - package.json - yarn.lock #### Note for [zero-installs](https://yarnpkg.com/features/zero-installs) users If you are using the Yarn feature [zero-installs](https://yarnpkg.com/features/zero-installs) that was introduced in Yarn V2, note that this PR does not update the `.yarn/cache/` directory meaning this code cannot be pulled and immediately developed on as one would expect for a zero-install project - you will need to run `yarn` to update the contents of the `./yarn/cache` directory. If you are not using zero-install you can ignore this as your flow should likely be unchanged. #### Vulnerabilities that will be fixed ##### With an upgrade: Severity | Priority Score (*) | Issue | Breaking Change | Exploit Maturity :-------------------------:|-------------------------|:-------------------------|:-------------------------|:-------------------------  | **601/1000** <br/> **Why?** Recently disclosed, Has a fix available, CVSS 6.3 | Cross-site Scripting (XSS) <br/>[SNYK-JS-COOKIE-8163060](https://snyk.io/vuln/SNYK-JS-COOKIE-8163060) | 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. ------------ **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: <img src="https://api.segment.io/v1/pixel/track?data=eyJ3cml0ZUtleSI6InJyWmxZcEdHY2RyTHZsb0lYd0dUcVg4WkFRTnNCOUEwIiwiYW5vbnltb3VzSWQiOiI5NmUzZTQzNS1jNTQxLTQzYWQtYWJmZC1hNTAzMjNjZjJjMjEiLCJldmVudCI6IlBSIHZpZXdlZCIsInByb3BlcnRpZXMiOnsicHJJZCI6Ijk2ZTNlNDM1LWM1NDEtNDNhZC1hYmZkLWE1MDMyM2NmMmMyMSJ9fQ==" width="0" height="0"/> 🧐 [View latest project report](https://app.snyk.io/org/mattbdean/project/400b3ef9-2e38-48de-8472-ec4332dca0a0?utm_source&#x3D;github&amp;utm_medium&#x3D;referral&amp;page&#x3D;fix-pr) 🛠 [Adjust project settings](https://app.snyk.io/org/mattbdean/project/400b3ef9-2e38-48de-8472-ec4332dca0a0?utm_source&#x3D;github&amp;utm_medium&#x3D;referral&amp;page&#x3D;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":"96e3e435-c541-43ad-abfd-a50323cf2c21","prPublicId":"96e3e435-c541-43ad-abfd-a50323cf2c21","dependencies":[{"name":"express","from":"4.16.4","to":"4.21.1"}],"packageManager":"yarn","projectPublicId":"400b3ef9-2e38-48de-8472-ec4332dca0a0","projectUrl":"https://app.snyk.io/org/mattbdean/project/400b3ef9-2e38-48de-8472-ec4332dca0a0?utm_source=github&utm_medium=referral&page=fix-pr","type":"auto","patch":[],"vulns":["SNYK-JS-COOKIE-8163060"],"upgrade":["SNYK-JS-COOKIE-8163060"],"isBreakingChange":false,"env":"prod","prType":"fix","templateVariants":["updated-fix-title","priorityScore"],"priorityScoreList":[601],"remediationStrategy":"vuln"}) --- **Learn how to fix vulnerabilities with free interactive lessons:** 🦉 [Cross-site Scripting (XSS)](https://learn.snyk.io/lesson/dom-based-xss/?loc&#x3D;fix-pr)