Bump tokio from 1.7.1 to 1.8.1 (#77)

Bumps [tokio](https://github.com/tokio-rs/tokio) from 1.7.1 to 1.8.1.
- [Release notes](https://github.com/tokio-rs/tokio/releases)
- [Commits](tokio-rs/tokio@tokio-1.7.1...tokio-1.8.1)

---
updated-dependencies:
- dependency-name: tokio
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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