Fixed a typo

Author: Fardin

2-ui/5-loading/01-onload-ondomcontentloaded/article.md

@@ -88,7 +88,7 @@ But there's a pitfall. If we have a script after the style, then that script mus
 ```html run
 <link type="text/css" rel="stylesheet" href="style.css">
 <script>
-  // the script doesn't not execute until the stylesheet is loaded
+  // the script doesn't execute until the stylesheet is loaded
   alert(getComputedStyle(document.body).marginTop);
 </script>
 ```