message: use hex::encode
diff: use errors::prelude::*;
  use services::ledger::merkletree::proof::{Lemma, Proof};
  use services::ledger::merkletree::tree::{LeavesIntoIterator, LeavesIterator, Tree, TreeLeafData};
  -use utils::crypto::hash::{Hash, HASHBYTES, EMPTY_HASH_BYTES};
  +use utils::crypto::hash::{Hash, EMPTY_HASH_BYTES};
  /// A Merkle tree is a binary tree, with values of type `T` at the leafs,
  /// and where every internal node holds the hash of the concatenation of the hashes of its children nodes.
  @@ -102,12 +102,7 @@ impl MerkleTree {
  /// Returns the hex root hash of Merkle tree
  pub fn root_hash_hex(&self) -> String {
  - let rh = self.root.hash();
  - let mut ret:String = String::with_capacity(HASHBYTES *2);
  - for i in rh {
  - ret.push_str(&format!("{:02x}", i));
  - }
  - ret
  + hex::encode(self.root.hash())
  }
  /// Returns the height of Merkle tree
  