updates default field prop to use Unix milliseconds format

Author: joshcarr

src/DateTimeField.jsx

@@ -18,7 +18,7 @@ DateTimeField = React.createClass({
  getDefaultProps: function() {
  return {
  dateTime: "1234567",
- format: 'X',
+ format: 'x',
  inputFormat: "MM/DD/YY H:mm A",
  showToday: true,
  viewMode: 'days',