Date error

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap-theme.min.css">
<script src="https://code.jquery.com/jquery-1.12.2.min.js"></script>
<script src="https://cdn.jsdelivr.net/jquery.validation/1.15.0/jquery.validate.js"></script>
<form id="user-register-form" action="/register/user">
  <div class="form-group">
    <label class="col-xs-12 col-sm-4 control-label" for="bornday">Tanggal Lahir<span class="text-red">*</span></label>
    <div class="col-sm-8">
      <div class="row">
        <div class="col-sm-3 col-xs-4">
          <select name="bornday" class="form-control input-w" required>
            <option value="">Tanggal</option>
            <option value="2">2</option>
            <option value="2">3</option>
          </select>
        </div>
        <div class="col-sm-3 col-xs-4">
          <select name="bornmonth" class="form-control input-w" required>
            <option value="">Bulan</option>
            <option value="2">2</option>
            <option value="2">3</option>
          </select>
        </div>
        <div class="col-sm-3 col-xs-4">
          <select name="bornyear" class="form-control input-w" required>
            <option value="">Tahun</option>
            <option value="2">1990</option>
            <option value="2">1991</option>
          </select>
        </div>
      </div>
    </div>
  </div>

  <button class="btn btn-edumor-secondary btn-fixed-width" name="submit">Daftar</button>

</form>

JavaScript

//jquery validation plugin
$('#user-register-form').validate({
  rules: {
    fullname: {
      minlength: 3,
      required: true
    },
    email: {
      email: true
    },
    password: {
      minlength: 8,
      required: true
    },
    bornday: {
      required: true
    },
    bornmonth: {
      required: true
    },
    bornyear: {
      required: true
    }
  },
  highlight: function(element) {
    $(element).parents('.form-group').addClass('has-error');
  },
  unhighlight: function(element) {
    $(element).parents('.form-group').removeClass('has-error');
  },
  errorElement: 'span',
  errorClass: 'validation-error-message help-block form-helper bold',
  errorPlacement: function(error, element) {
    if (element.parent('.input-group').length) {
      error.insertAfter(element.parent());
    } else {
      error.insertAfter(element);
    }
  }
});