Fix Apps onClick handler.

react-again-tutorial/src/App.tsx

@@ -13,7 +13,7 @@ function App() {
   const myClickHandlerMan = (event: MouseEvent) => {
     console.log(event);
 
-    setActiveListItem(event.target.key);
+    setActiveListItem(2);
   };
 
   return (
@@ -28,7 +28,7 @@ function App() {
                 : "list-group-item"
             }
             key={item}
-            onClick={myClickHandlerMan}
+            onClick={() => setActiveListItem(index)}
           >
             {item}
           </li>