build(deps): bump https-proxy-agent in /examples/lb3-express (#17)

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](TooTallNate/proxy-agents@2.2.1...2.2.4)

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