Bump h2 from 0.3.14 to 0.3.21

Bumps [h2](https://github.com/hyperium/h2) from 0.3.14 to 0.3.21.
- [Release notes](https://github.com/hyperium/h2/releases)
- [Changelog](https://github.com/hyperium/h2/blob/master/CHANGELOG.md)
- [Commits](hyperium/h2@v0.3.14...v0.3.21)

---
updated-dependencies:
- dependency-name: h2
  dependency-type: indirect
...

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