Mark scrollToEnd animated as optional

Summary:
The flow type and inheriting TS types mark animated as optional, mark it here as well.

Changelog:
[General][Fixed] - Mark scrollToEnd animated as optional

Reviewed By: christophpurrer

Differential Revision: D42036647

fbshipit-source-id: 59d408adc639ee1e0ca040301511c64d7ba55bfe

Libraries/Components/ScrollView/ScrollView.d.ts

@@ -841,7 +841,7 @@ export class ScrollView extends ScrollViewBase {
    * The options object has an animated prop, that enables the scrolling animation or not.
    * The animated prop defaults to true
    */
-  scrollToEnd(options?: {animated: boolean}): void;
+  scrollToEnd(options?: {animated?: boolean}): void;
 
   /**
    * Displays the scroll indicators momentarily.