Update array stack.

docs/chapter_stack_and_queue/queue.md

@@ -264,7 +264,7 @@ comments: true
         /* 访问队首元素 */
         public int peek() {
             if (size() == 0)
-                throw new IndexOutOfBoundsException();
+                throw new EmptyStackException();
             return front.val;
         }
     }