code: function mnemonicToPubKey(str) {
  
    var m = new Mnemonic(str);
  
    var xpriv1 = m.toHDPrivateKey(); // no passphrase
  
    var xpub1 = xpriv1.hdPublicKey;
  
    return xpub1
  }
docs: get a public key from a mnemonic
  @param  {String} str The mnemonic
  @return {Object}     The HD Public Key