Update hellox3dom.html

public/X3DOMTutorial/hellox3dom.html

@@ -5,7 +5,7 @@
   <title> Hello X3DOM </title>
   <link rel="stylesheet" type="text/css" href="x3dom.css">
   </link>
-  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.5.1/styles/vs.min.css">
+  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.5.1/styles/vs.min.css"></link>
   <script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.5.1/highlight.min.js"></script>
   <script>hljs.highlightAll();</script>
 </head>