Bump nyholm/psr7 from 1.5.1 to 1.6.1 (#266)

Bumps [nyholm/psr7](https://github.com/Nyholm/psr7) from 1.5.1 to 1.6.1.
- [Release notes](https://github.com/Nyholm/psr7/releases)
- [Changelog](https://github.com/Nyholm/psr7/blob/master/CHANGELOG.md)
- [Commits](Nyholm/psr7@1.5.1...1.6.1)

---
updated-dependencies:
- dependency-name: nyholm/psr7
  dependency-type: direct:production
...

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