Bump github.com/ipfs/go-merkledag from 0.8.0 to 0.8.1

Bumps [github.com/ipfs/go-merkledag](https://github.com/ipfs/go-merkledag) from 0.8.0 to 0.8.1.
- [Release notes](https://github.com/ipfs/go-merkledag/releases)
- [Commits](ipfs/go-merkledag@v0.8.0...v0.8.1)

---
updated-dependencies:
- dependency-name: github.com/ipfs/go-merkledag
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]