Fix misuse of second argument as nextState (the actual argument is prevState)

This fixes instances where, right after scrolling, a change in the
`scrollToIndex` prop will not actually scroll to the item at the passed
index correctly. This is due to the `componentDidUpdate` method
considering the previous state to actually be the next state and
looking at `scrollChangeReason` on it, seeing the old
`scrollChangeReason` caused by the user scrolling, thus not calling
`scrollTo` to actually center the element.

Author: gabrielecirulli

src/index.tsx

@@ -183,10 +183,10 @@ export default class VirtualList extends React.PureComponent<Props, State> {
     }
   }
 
-  componentDidUpdate(_: Props, nextState: State) {
-    const {offset} = this.state;
+  componentDidUpdate(_: Props, prevState: State) {
+    const {offset, scrollChangeReason} = this.state;
 
-    if (nextState.offset !== offset && nextState.scrollChangeReason === SCROLL_CHANGE_REQUESTED) {
+    if (prevState.offset !== offset && scrollChangeReason === SCROLL_CHANGE_REQUESTED) {
       this.scrollTo(offset);
     }
   }