Bump path-to-regexp from 1.8.0 to 1.9.0 in /docs (#1401)

Bumps [path-to-regexp](https://github.com/pillarjs/path-to-regexp) from 1.8.0 to 1.9.0.
- [Release notes](https://github.com/pillarjs/path-to-regexp/releases)
- [Changelog](https://github.com/pillarjs/path-to-regexp/blob/master/History.md)
- [Commits](pillarjs/path-to-regexp@v1.8.0...v1.9.0)

---
updated-dependencies:
- dependency-name: path-to-regexp
  dependency-type: indirect
...

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