Before markup :

<script>
$(function() {
$( "#check_in" ).datepicker({
 defaultDate: "+1w",
 changeMonth: true,
 minDate: 0,
 onClose: function( selectedDate ) {
  var selectedDate = $(this).datepicker('getDate');
            if (selectedDate) {
                  selectedDate.setDate(selectedDate.getDate() + 1);
            }
 $( "#check_out" ).datepicker( "option", "minDate", selectedDate );
 }
 });
$( "#check_out" ).datepicker({
 defaultDate: "+1w",
 changeMonth: true,
 minDate: 0,
 onClose: function( selectedDate ) {
 $( "#check_in" ).datepicker( "option", "maxDate", selectedDate );
 }
 });
});
</script>

Lastly found out markup
It help you to convert your code the code into HTML 


Used markup :

<script>
$(function() {
$( "#check_in" ).datepicker({
    defaultDate: "+1w",
    changeMonth: true,
    minDate: 0,
    onClose: function( selectedDate ) {
        var selectedDate = $(this).datepicker('getDate');
            if (selectedDate) {
                  selectedDate.setDate(selectedDate.getDate() + 1);
            }
    $( "#check_out" ).datepicker( "option", "minDate", selectedDate );
    }
    });
$( "#check_out" ).datepicker({
    defaultDate: "+1w",
    changeMonth: true,
    minDate: 0,
    onClose: function( selectedDate ) {
    $( "#check_in" ).datepicker( "option", "maxDate", selectedDate );
    }
    });
});
</script>