message: Use the `hash_pair()` utility fn in `root_hash()`
diff: @@ -152,17 +152,12 @@ impl IndexedMerkleProof {
  let mut acc = leaf_hash;
  for hash in hashes {
  - let mut hasher = VarBlake2b::new(Digest::LENGTH).unwrap();
  - if (path & 1) == 1 {
  - hasher.update(hash);
  - hasher.update(&acc);
  + let digest = if (path & 1) == 1 {
  + Digest::hash_pair(hash, &acc)
  } else {
  - hasher.update(&acc);
  - hasher.update(hash);
  - }
  - hasher.finalize_variable(|slice| {
  - acc.0.copy_from_slice(slice);
  - });
  + Digest::hash_pair(&acc, hash)
  + };
  + acc.0.copy_from_slice(digest.as_ref());
  path >>= 1;
  }
  acc
  