datepicker，结束时间必须大于开始时间

$('#js-start-time').datepicker({
	dateFormat:'yy-mm-dd',
	onSelect: function( startDate ) {
		var $startDate = $( "#js-start-time" );
		var $endDate = $('#js-end-time');
		var endDate = $endDate.datepicker( 'getDate' );
		if(endDate < startDate){
			$endDate.datepicker('setDate', startDate - 3600*1000*24);
		}
		$endDate.datepicker( "option", "minDate", startDate );
	}
});
$('#js-end-time').datepicker({
	dateFormat:'yy-mm-dd',
	onSelect: function( endDate ) {
		var $startDate = $( "#js-start-time" );
		var $endDate = $('#js-end-time');
		var startDate = $startDate.datepicker( "getDate" );
		if(endDate < startDate){
			$startDate.datepicker('setDate', startDate + 3600*1000*24);
		}
		$startDate.datepicker( "option", "maxDate", endDate );
	}
});