title: Pass ion-select-option to function - Ionic 4
body: <p>I have this <code>Ionic</code> version 4 code that is simply trying to take a the selected value and pass it to a function in it's component: </p>
  
  <pre><code>&lt;ion-item&gt;
  &lt;ion-label&gt;Convert Currency&lt;/ion-label&gt;
  &lt;ion-select [(ngModel)]="currency"&gt;
  &lt;ion-select-option *ngFor="let c of currencyData" [value] = "c" &gt;{{c.text}}&lt;/ion-select-option&gt;
  &lt;/ion-select&gt;
  </code></pre>
  
  <p></p>
  
  <p>I tried <code>onChange</code> but that is apparently not in version 4. </p>