Bump guzzlehttp/oauth-subscriber from 0.6.0 to 0.8.1

Bump guzzlehttp/oauth-subscriber from 0.6.0 to 0.8.1

Bumps [guzzlehttp/oauth-subscriber](https://github.com/guzzle/oauth-subscriber) from 0.6.0 to 0.8.1.
- [Release notes](https://github.com/guzzle/oauth-subscriber/releases)
- [Changelog](https://github.com/guzzle/oauth-subscriber/blob/0.8/CHANGELOG.md)
- [Commits](https://github.com/guzzle/oauth-subscriber/compare/0.6.0...0.8.1)

---
updated-dependencies:
- dependency-name: guzzlehttp/oauth-subscriber
  dependency-version: 0.8.1
  dependency-type: direct:production
...

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