title: NGX-Bootstrap: dropdown doesn't show the selected item
body: <p>I'd like to use ngx-angular dropdown. I've followed the installation instruction from <a href="https://valor-software.com/ngx-bootstrap/#/dropdowns" rel="nofollow noreferrer">their official page</a>. The dropdown is displaying, but when I select an item, it doesn't appear at the top like a regular dropdown. </p>
  
  <p>I can't find any working example online. Even on their official page, when you select an item, nothing happens. </p>
  
  <p>Can someone tell whether I need to add code to make it work?</p>
  
  <h1>EDIT</h1>
  
  <p>1) Initial state</p>
  
  <p><a href="https://i.stack.imgur.com/2E1TX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2E1TX.png" alt="enter image description here"></a></p>
  
  <p>2) Expend and Select any item</p>
  
  <p><a href="https://i.stack.imgur.com/BoTda.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BoTda.png" alt="enter image description here"></a></p>
  
  <p>3) Button Dropdown is still selected</p>
  
  <p><a href="https://i.stack.imgur.com/2E1TX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2E1TX.png" alt="enter image description here"></a></p>
  
  <p>Is this how it's supposed to work?</p>