title: Adding active class for nav-link
body: <p>I need to add an active class to the .nav-link inside the parent nav-item if any of the sub-menu is active.</p>
  
  <pre><code>&lt;ul&gt;
      &lt;li class="nav-item"&gt;
          &lt;a class="nav-link" (click)="BEDropdownOpen = !BEDropdownOpen" [attr.aria-expanded]="BEDropdownOpen"
              aria-controls="basic-elements-dropdown"&gt;
              Elements
          &lt;/a&gt;
          &lt;div class="collapse" id="basic-elements-dropdown" [ngbCollapse]="!BEDropdownOpen"&gt;
              &lt;ul class="nav flex-column sub-menu"&gt;
                  &lt;li class="nav-item"&gt;
                      &lt;a class="nav-link" routerLink="/accordions" routerLinkActive="active"&gt;Accordion&lt;/a&gt;
                  &lt;/li&gt;
                  &lt;li class="nav-item"&gt;
                      &lt;a class="nav-link" routerLink="/typography" routerLinkActive="active"&gt;Typography&lt;/a&gt;
                  &lt;/li&gt;
                  &lt;li class="nav-item"&gt;
                      &lt;a class="nav-link" routerLink="/tooltips" routerLinkActive="active"&gt;Tooltip&lt;/a&gt;
                  &lt;/li&gt;
              &lt;/ul&gt;
          &lt;/div&gt;
      &lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>If any of the .nav-link inside the div.collapse has an active class,
  an active class should be added to the nav-link inside the parent nav-item</p>