Changed url of interactive GitHub courses

Author: MekDrop

README.md

@@ -50,6 +50,6 @@ if ($instance instanceof ToArrayInterface) {
 
 ## How to contribute?
 
-If you want to add some functionality or fix bugs, you can fork, change and create pull request. If you not sure how this works, try [interactive GitHub tutorial](https://try.github.io).
+If you want to add some functionality or fix bugs, you can fork, change and create pull request. If you not sure how this works, try [interactive GitHub tutorial](https://skills.github.com).
 
 If you found any bug or have some questions, use [issues tab](https://github.com/imponeer/toarray-interface/issues) and write there your questions.