Bump proxy-addr from 2.0.6 to 2.0.8 in /react-express-mongodb/backend

Bumps [proxy-addr](https://github.com/jshttp/proxy-addr) from 2.0.6 to 2.0.8.
- [Release notes](https://github.com/jshttp/proxy-addr/releases)
- [Changelog](https://github.com/jshttp/proxy-addr/blob/master/HISTORY.md)
- [Commits](https://github.com/jshttp/proxy-addr/compare/v2.0.6...v2.0.8)

---
updated-dependencies:
- dependency-name: proxy-addr
  dependency-version: 2.0.8
  dependency-type: indirect
...

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