Fix typo

Author: Violet-Bora-Lee

1-js/13-modules/02-import-export/article.md

@@ -151,7 +151,7 @@ say.*!*hi*/!*('John'); // Hello, John!
 say.*!*bye*/!*('John'); // Bye, John!
 ```
 
-## export default
+## Export default
 
 In practice, there are mainly two kinds of modules.