fix too many siblings activation in scrollspy

Created by: mr-july

if the scrollspy applied to hierarchical navigation, then too many nav-links are activated. Example markup:

<ul id="toc" class="bs-sidenav nav">
  <li>
    <a href="#v1" class="nav-link">Volume 1</a>
    <ul class="nav">
      <li>
        <a href="#ch-1-1" class="nav-link">Chapter 1.1</a>
      </li>
      <li>
        <a href="#ch-1-2" class="nav-link">Chapter 1.2</a>
      </li>
      <li>
        <a href="#ch-1-3" class="nav-link">Chapter 1.3</a>
      </li>
    </ul>
  </li>
  <li>
    <a href="#v2" class="nav-link">Volume 2</a>
    <ul class="nav">
      <li>
        <a href="#ch-2-1" class="nav-link">Chapter 2.1</a>
      </li>
      <li>
        <a href="#ch-2-2" class="nav-link">Chapter 2.2</a>
      </li>
    </ul>
  </li>
</ul>

on activation of "Chapter 1.2" all siblings ("Chapter 1.1" and "Chapter 1.3") are also activated, because the selector

$('.nav-link[href="#ch-1-2"]').parents('li').find('.nav-links')

matches all ".nav-link"s under "#v1", so the correct selector should be

$('.nav-link[href="#ch-1-2"]').parents('li').find('> .nav-links')
                                                   ^
                                      only direct children of li