message: refactor(core): use bip32 in transactionBuilder
  Issue:
diff: // Copyright 2014, BitGo, Inc. All Rights Reserved.
  //
  +import * as bip32 from 'bip32';
  import * as Bluebird from 'bluebird';
  import * as bitcoin from '@bitgo/utxo-lib';
  import * as _ from 'lodash';
  @@ -897,7 +898,7 @@ exports.signTransaction = function (params) {
  let rootExtKey;
  if (keychain) {
  - rootExtKey = bitcoin.HDNode.fromBase58(keychain.xprv);
  + rootExtKey = bip32.fromBase58(keychain.xprv);
  }
  const txb = bitcoin.TransactionBuilder.fromTransaction(transaction, network);
  @@ -922,7 +923,7 @@ exports.signTransaction = function (params) {
  if (rootExtKey) {
  const { walletSubPath = '/0/0' } = keychain;
  const path = sanitizeLegacyPath(keychain.path + walletSubPath + chainPath);
  - privKey = rootExtKey.derivePath(path).keyPair;
  + privKey = rootExtKey.derivePath(path);
  }
  privKey.network = network;
  