[docs] adjust function name (#6495)

site/content/tutorial/02-reactivity/01-reactive-assignments/app-a/App.svelte

@@ -1,11 +1,11 @@
 <script>
 	let count = 0;
 
-	function handleClick() {
+	function incrementCount() {
 		// event handler code goes here
 	}
 </script>
 
 <button>
 	Clicked {count} {count === 1 ? 'time' : 'times'}
-</button>
+</button>