Update README.md

Author: adrianhajdin

README.md

@@ -2,7 +2,7 @@
 
 ### [Live Site](https://realtime-chat-application.netlify.com)
 
-### [🌟 Become a top 1% Next.js 13 developer in only one course](https://jsmastery.pro/next13)
+### [🌟 Become a top 1% Next.js developer in only one course](https://jsmastery.pro/next15)
 ### [🚀 Land your dream programming job in 6 months](https://jsmastery.pro/masterclass)
 
 ![Chat Application](https://i.ytimg.com/vi/ZwFA3YMfkoc/maxresdefault.jpg)