Fix LI content numbers

I think this is more convenient. If one will call chapter.closest('.chapter') they will understand that it returns the first <li class="chapter">

Author: Vitruvius21

2-ui/1-document/04-searching-elements-dom/article.md

@@ -154,7 +154,7 @@ For instance:
 <div class="contents">
   <ul class="book">
     <li class="chapter">Chapter 1</li>
-    <li class="chapter">Chapter 1</li>
+    <li class="chapter">Chapter 2</li>
   </ul>
 </div>