Update article.md

Hi guys, I looked at your article to solve my CORS issue but it didn't work. So eventually I found a question on StackOverflow that explained in order to make things work properly, I needed to add also "Access-Control-Allow-Origin: https://javascript.info" to the preflight response. Did anyone have the same issue? If so, we need to update the article in order to save the time of future readers :)

StackOverflow question: https://stackoverflow.com/questions/42558221/how-to-cors-enable-apache-web-server-including-preflight-and-custom-headers

Author: cristian-wang

5-network/05-fetch-crossorigin/article.md

@@ -259,6 +259,7 @@ Access-Control-Request-Headers: Content-Type,API-Key
 ### Step 2 (preflight response)
 
 The server should respond with status 200 and headers:
+- `Access-Control-Allow-Origin: https://javascript.info`
 - `Access-Control-Allow-Methods: PATCH`
 - `Access-Control-Allow-Headers: Content-Type,API-Key`.