Bump github.com/docker/distribution (#179)

Bumps [github.com/docker/distribution](https://github.com/docker/distribution) from 2.7.1+incompatible to 2.8.0+incompatible.
- [Release notes](https://github.com/docker/distribution/releases)
- [Commits](https://github.com/docker/distribution/compare/v2.7.1...v2.8.0

)

---
updated-dependencies:
- dependency-name: github.com/docker/distribution
  dependency-type: direct:production
...

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