title: Change styles on ngb-tab title
body: <p>I would like to style the title in ngb-tab so that it is not the default blue of an anchor tag. Ideally something like this, but the class property doesn't seem to have an effect on ngb-tab.</p>
  
  <p>The HTML:</p>
  
  <pre><code>&lt;ngb-tabset #t="ngbTabset"&gt;
      &lt;ngb-tab [title]="'Followers'" class="tab-title"&gt;
          &lt;ng-template ngbTabContent&gt;
              ...
          &lt;/ng-template&gt;
      &lt;/ngb-tab&gt;
      &lt;ngb-tab [title]="'Following'" class="tab-title"&gt;
          &lt;ng-template ngbTabContent&gt;
              ...
          &lt;/ng-template&gt;
      &lt;/ngb-tab&gt;
  &lt;/ngb-tabset&gt;
  </code></pre>
  
  <p>The CSS:</p>
  
  <pre><code>.tab-title {
    color: inherit;
  }
  </code></pre>