message: fix(sortable): make property public for AoT compilance
  fixes
diff: @@ -80,9 +80,9 @@ export class SortableComponent implements ControlValueAccessor {
  */
  @Output() public onChange: EventEmitter<any[]> = new EventEmitter<any[]>();
  - private _items: SortableItem[];
  + public showPlaceholder: boolean = false;
  - private showPlaceholder: boolean = false;
  + private _items: SortableItem[];
  private get items(): SortableItem[] {
  return this._items;
  