DataGrid: fix Angular code in Customize Buttons (DevExpress#6932) (DevExpress#6933)

Author: vladaskorohodova

concepts/05 UI Components/DataGrid/15 Columns/10 Column Types/4 Command Columns/15 Customize the Edit Column/1 Customize Buttons.md

@@ -158,7 +158,7 @@ You can also declare custom logic in the button configuration. For instance, the
         <dxi-column type="buttons">
             <dxi-button
                 name="edit"
-                (onClick)="onEditButtonClick($event)">
+                [onClick]="onEditButtonClick">
             </dxi-button>
             <dxi-button name="delete"></dxi-button>
         </dxi-column>