title: Angular 9 error mde-popover is not a known element
body: <p>I am working with angular 9 and I want to have a popover with a delete and edit option in it whenever someone hovers over a <code>mat-card</code>. I imported <code>mdePopoverModule</code> in <code>app.module.ts</code> but when I want to use <code>&lt;mde-popover&gt;</code></p>
  <p>it gives me this error :</p>
  <p><a href="https://i.stack.imgur.com/4u99L.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4u99L.png" alt="enter image description here" /></a></p>
  <p>HTML :</p>
  <pre><code>&lt;mat-card 
    [mdePopoverTriggerFor]=&quot;appPopover&quot; 
    class=&quot;skill-name&quot; 
    *ngFor=&quot;let skillcard of skillcolumn.items&quot;&gt;
    &lt;mat-card-content&gt;{{skillcard.skill}}&lt;/mat-card-content&gt;
  &lt;/mat-card&gt;
  
  &lt;mde-popover #appPopover=&quot;mdePopover&quot;&gt;
    &lt;p&gt;test &lt;/p&gt;
  &lt;/mde-popover&gt;
  </code></pre>
  <p>app.module.ts</p>
  <pre><code>import { MdePopoverModule } from '@material-extended/mde';
  
  @NgModule({
    declarations: [AppComponent],
    imports: [
      BrowserModule,
      AppRoutingModule,
      FlexLayoutModule,
      BrowserAnimationsModule,
      MyMaterialModule,
      MdePopoverModule,
    ],
  </code></pre>
  <p>Anyone who knows what I could do to fix this error?</p>