title: Lo-Dash sortBy array of dates in string format
body: <p>I'd like to know why lodash doesn't sort array of dates in string format as compared with plain javascript <code>sort()</code>. Is it expected behavior or a bug?</p>
  
  <pre><code>var array = ["2014-11-11", "2014-11-12", null, "2014-11-01", null, null, "2014-11-05"];
  
  _.sortBy(array);
  // ["2014-11-11", "2014-11-12", null, "2014-11-01", null, null, "2014-11-05"]
  
  _.sortBy(array, function(value) {return new Date(value);});
  // [null, null, null, "2014-11-01", "2014-11-05", "2014-11-11", "2014-11-12"]
  
  array.sort();
  // ["2014-11-01", "2014-11-05", "2014-11-11", "2014-11-12", null, null, null]
  </code></pre>
  
  <p>Version used: Lo-Dash v2.4.1 – Modern build.</p>