title: ng-select inside ngx-datatable dropdown is not visible
body: <p>(I reproduced my issue here: <a href="https://plnkr.co/QvEWjhJhbsghy1OD" rel="nofollow noreferrer">https://plnkr.co/QvEWjhJhbsghy1OD</a>)</p>
  
  <p>The <code>&lt;ng-select&gt;</code> drop down list of options is not displayed "over' the <code>&lt;ngx-datatable&gt;</code> row, it seems cut by the cell's height, making it pretty useless. </p>
  
  <p><a href="https://i.stack.imgur.com/Im6sE.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Im6sE.png" alt="cut off ng-select"></a></p>
  
  <p>A regular <code>&lt;select&gt;</code> works fine though, I can see all options.</p>
  
  <p><a href="https://i.stack.imgur.com/tx1XH.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tx1XH.png" alt="working regular select"></a></p>
  
  <p>How can I make the ng-select works as expected?</p>