fix typo

lib/hdprivatekey.js

@@ -88,7 +88,7 @@ HDPrivateKey.isValidPath = function(arg, hardened) {
 /**
  * Internal function that splits a string path into a derivation index array.
  * It will return null if the string path is malformed.
- * It does not validates if a indexes are in bounds.
+ * It does not validate if indexes are in bounds.
  *
  * @param {string} path
  * @return {Array}