Bump guzzlehttp/psr7 from 1.9.0 to 1.9.1 in /example

Bumps [guzzlehttp/psr7](https://github.com/guzzle/psr7) from 1.9.0 to 1.9.1.
- [Release notes](https://github.com/guzzle/psr7/releases)
- [Changelog](https://github.com/guzzle/psr7/blob/1.9.1/CHANGELOG.md)
- [Commits](guzzle/psr7@1.9.0...1.9.1)

---
updated-dependencies:
- dependency-name: guzzlehttp/psr7
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]