Nested structure not supported

[nifanic]

Nice component, but doesn't seem supporting nested HTML structure, like—

<chapter>
  <header id="section1">Chapter 1</header>
  <main>
    <section>
      <header id="subheaderA">Subheader A</header>
    </section>
    <section>
      <header id="subheaderB">Subheader B</header>
    </section>
  </main>
</chapter>

In this example, if we are on Subheader A, react-ui-scrollspy will still highlight Chapter 1 as active.