Update README.md

README.md

@@ -21,7 +21,7 @@ recommend using the [app skeleton](https://github.com/cakephp/app) as
 a starting point. For existing applications you can run the following:
 
 ``` bash
-$ composer require cakephp/cakephp:"~3.3"
+$ composer require cakephp/cakephp:"~3.4"
 ```
 
 ## Running Tests