Formatting Dates YYYY-MM-DD

// data stolen from http://howmanyleft.co.uk/vehicle/jaguar_'e'_type
var day_data = [
  {"period": "2012-10-01", "licensed": 3407, "sorned": 660},
  {"period": "2011-08-12", "licensed": 3351, "sorned": 629},
  {"period": "2011-03-03", "licensed": 3269, "sorned": 618},
  {"period": "2010-08-08", "licensed": 3246, "sorned": 661},
  {"period": "2010-05-10", "licensed": 3257, "sorned": 667},
  {"period": "2010-03-14", "licensed": 3248, "sorned": 627},
  {"period": "2010-01-10", "licensed": 3171, "sorned": 660},
  {"period": "2009-12-10", "licensed": 3171, "sorned": 676},
  {"period": "2009-10-07", "licensed": 3201, "sorned": 656},
  {"period": "2009-09-25", "licensed": 3215, "sorned": 622},
];
Morris.Line({
  element: 'graph',
  data: day_data,
  xkey: 'period',
  ykeys: ['licensed', 'sorned'],
  labels: ['Licensed', 'SORN']
});