Update the checkbox example so when user make checkbox checked, the (#6066)

upper part is updated

Author: tinayuangao

src/material-examples/checkbox-configurable/checkbox-configurable-example.html

@@ -28,8 +28,8 @@ <h2 class="example-h2">Result</h2>
     <section class="example-section">
       <md-checkbox
           class="example-margin"
-          [checked]="checked"
-          [indeterminate]="indeterminate"
+          [(ngModel)]="checked"
+          [(indeterminate)]="indeterminate"
           [align]="align"
           [disabled]="disabled">
         I'm a checkbox