Update sha2 requirement from 0.9 to 0.10 (#1071)

* Update sha2 requirement from 0.9 to 0.10

Updates the requirements on [sha2](https://github.com/RustCrypto/hashes) to permit the latest version.
- [Release notes](https://github.com/RustCrypto/hashes/releases)
- [Commits](https://github.com/RustCrypto/hashes/compare/groestl-v0.9.0...sha2-v0.10.0

)

---
updated-dependencies:
- dependency-name: sha2
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

* Use `Digest` trait over `FixedOutput`

The `Digest` trait is now a wrapper around `FixedOutput` (among others),
so we only need to keep `Digest` around.

* RustFmt

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Hernando Castano <hernando@hcastano.com>