Update README.md

Author: dereuromark

README.md

@@ -32,4 +32,4 @@ For bugs and feature requests, please use the [issues](https://github.com/dereur
 To contribute to this plugin please follow a few basic rules.
 
 * Pull requests must be sent to the branch that reflects the version you want to contribute to.
-* [Unit tests](http://book.cakephp.org/5.0/en/development/testing.html) are required.
+* [Unit tests](http://book.cakephp.org/5/en/development/testing.html) are required.