Bootstrap Modal Focus not working

while making a web I didn't get focus in a "input" into Bootstrap Modal, I tried everything and didn't work, modal appears but input doesn't get focus. I have make a "test.php" with a simple modal and doesn't work either. Here is the "test.php"

<html lang="es">

<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">


    <link href="../css/bootstrap.min.css" rel="stylesheet">
    <script src="../js/jquery.min.js"></script>
    <script src="../js/bootstrap.min.js">



    <script>


$('#myModal').on('shown.bs.modal', function () {
    $('#referencia').focus();
})


    </script>

</head>
<body>
<!-- Button trigger modal -->
<button type="button" class="btn btn-primary btn-lg" data-toggle="modal" data-target="#myModal">
  Launch demo modal
</button>

<!-- Modal -->
<div class="modal fade" id="myModal">
  <div class="modal-dialog">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
        <h4 class="modal-title">Modal title</h4>
      </div>
      <div class="modal-body">
        <input name="referencia" id="referencia" type="text" class="form-control text-uppercase" placeholder="Descripci&oacute;n">
      </div>
      <div class="modal-footer">
        <button type="button" class="btn btn-default" data-dismiss="modal">Close</button>
        <button type="button" class="btn btn-primary">Save changes</button>
      </div>
    </div><!-- /.modal-content -->
  </div><!-- /.modal-dialog -->
</div><!-- /.modal -->
</body>

If I try this code on my server it doesn't work, on unelink.es server doesn't work either, but if I put the same code on "fiddle", works fine.

Any idea of what is wrong? If I need something else... or install something in server.

P.D. Sorry for my English.

Try this (autofocus added to your link):

<input name="referencia" id="referencia" type="text" class="form-control text-uppercase" placeholder="Descripci&oacute;n" autofocus>

or try this:

$('#myModal').on('shown.bs.modal', function () {
    $('#myInput').focus();
})

or this:

// Every time a modal is shown, if it has an autofocus element, focus on it.
$('.modal').on('shown.bs.modal', function() {
  $(this).find('[autofocus]').focus();
});