Bump https-proxy-agent from 2.2.1 to 2.2.4 in /dashboard/assets

Bumps [https-proxy-agent](https://github.com/TooTallNate/node-https-proxy-agent) from 2.2.1 to 2.2.4.
- [Release notes](https://github.com/TooTallNate/node-https-proxy-agent/releases)
- [Commits](https://github.com/TooTallNate/node-https-proxy-agent/compare/2.2.1...2.2.4

)

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