fix(file-list): use lodash find()

Use lodash find() instead of ES6 Array.prototype.find.
ES6 find is not available on standard node installations
(without the harmony flag)

Closes #1533

lib/file-list.js

@@ -99,7 +99,7 @@ List.prototype._isExcluded = function (path) {
 //
 // Returns the match or `undefined` if none found.
 List.prototype._isIncluded = function (path) {
-  return this._patterns.find(function (pattern) {
+  return _.find(this._patterns, function (pattern) {
     return mm(path, pattern.pattern)
   })
 }
@@ -133,7 +133,7 @@ List.prototype._exists = function (path) {
     return mm(path, pattern.pattern)
   })
 
-  return !!patterns.find(function (pattern) {
+  return !!_.find(patterns, function (pattern) {
     return self._findFile(path, pattern)
   })
 }