Bump async-trait from 0.1.56 to 0.1.57 (paritytech#802)

Bumps [async-trait](https://github.com/dtolnay/async-trait) from 0.1.56 to 0.1.57.
- [Release notes](https://github.com/dtolnay/async-trait/releases)
- [Commits](dtolnay/async-trait@0.1.56...0.1.57)

---
updated-dependencies:
- dependency-name: async-trait
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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