title: Bootstrap accordion not working if ID is number
body: <p>I have problems after upgrading Bootstrap to 4.2.1 version. In this version when I use <code>id="#12"</code> in <code>accordion</code> it's not working. In previous versions it worked fine with <code>id="#12"</code>. Any ideas?</p>
  
  <pre><code>  &lt;div id="accordion"&gt;
      &lt;div class="card"&gt;
    &lt;div class="card-header" id="headingOne"&gt;
       &lt;h5 class="mb-0"&gt;
          &lt;button class="btn btn-link" data-toggle="collapse" data-target="#12"
             aria-expanded="true" aria-controls="collapseOne"&gt;
          Collapsible Group Item #1
          &lt;/button&gt;
       &lt;/h5&gt;
    &lt;/div&gt;
    &lt;div id="12" class="collapse show" aria-labelledby="headingOne" data-parent="#accordion"&gt;
       &lt;div class="card-body"&gt;
          Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry
          richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard
          dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf
          moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla
          assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore
          wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher
          vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic
          synth nesciunt you probably haven't heard of them accusamus labore
          sustainable VHS.
       &lt;/div&gt;
    &lt;/div&gt;
  </code></pre>
  
  <p>
  </p>