ts grammar fix (#181)

Author: xifeiwu

examples/height.tsx

@@ -6,7 +6,7 @@ interface Item {
   height: number;
 }
 
-const MyItem: React.FC<Item> = ({ id, height }, ref) => {
+const MyItem: React.ForwardRefRenderFunction<HTMLElement, Item> = ({ id, height }, ref) => {
   return (
     <span
       ref={ref}

src/ScrollBar.tsx

@@ -33,7 +33,7 @@ export default class ScrollBar extends React.Component<ScrollBarProps, ScrollBar
 
   thumbRef = React.createRef<HTMLDivElement>();
 
-  visibleTimeout: NodeJS.Timeout = null;
+  visibleTimeout: ReturnType<typeof setTimeout> = null;
 
   state: ScrollBarState = {
     dragging: false,