Update article.md

Author: atulsm

1-js/02-first-steps/16-javascript-specials/article.md

@@ -102,7 +102,7 @@ More in: <info:variables> and <info:types>.
 
 We're using a browser as a working environment, so basic UI functions will be:
 
-[`prompt(question[, default])`](mdn:api/Window/prompt)
+[`prompt(question, [default])`](mdn:api/Window/prompt)
 : Ask a `question`, and return either what the visitor entered or `null` if they pressed "cancel".
 
 [`confirm(question)`](mdn:api/Window/confirm)