Bump on-headers and compression in /site (#612)

Bumps [on-headers](https://github.com/jshttp/on-headers) and [compression](https://github.com/expressjs/compression). These dependencies needed to be updated together.

Updates `on-headers` from 1.0.2 to 1.1.0
- [Release notes](https://github.com/jshttp/on-headers/releases)
- [Changelog](https://github.com/jshttp/on-headers/blob/master/HISTORY.md)
- [Commits](jshttp/on-headers@v1.0.2...v1.1.0)

Updates `compression` from 1.8.0 to 1.8.1
- [Release notes](https://github.com/expressjs/compression/releases)
- [Changelog](https://github.com/expressjs/compression/blob/master/HISTORY.md)
- [Commits](expressjs/compression@1.8.0...v1.8.1)

---
updated-dependencies:
- dependency-name: on-headers
  dependency-version: 1.1.0
  dependency-type: indirect
- dependency-name: compression
  dependency-version: 1.8.1
  dependency-type: indirect
...

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Author: dependabot[bot]