Add optional flags for callbacks

Author: Marek Rozmus

src/module.d.ts

@@ -20,9 +20,9 @@ interface ISwipeableListItemProps {
   scrollStartThreshold?: number;
   swipeStartThreshold?: number;
   threshold?: number;
-  onSwipeStart: () => void;
-  onSwipeEnd: () => void;
-  onSwipeProgress: (progress: number) => void;
+  onSwipeStart?: () => void;
+  onSwipeEnd?: () => void;
+  onSwipeProgress?: (progress: number) => void;
 }
 
 export class SwipeableListItem extends React.Component<