build(deps): bump keccak from 0.1.5 to 0.1.6

Bumps [keccak](https://github.com/RustCrypto/sponges) from 0.1.5 to 0.1.6.
- [Commits](RustCrypto/sponges@keccak-v0.1.5...keccak-v0.1.6)

---
updated-dependencies:
- dependency-name: keccak
  dependency-version: 0.1.6
  dependency-type: indirect
...

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

Author: dependabot[bot]