Update README.md

Author: Holt59

README.md

@@ -24,7 +24,7 @@ composer require holt59/cakephp3-bootstrap-helpers:~3.0*
 
 If you want to test the **Bootstrap 4** version of the plugin (alpha):
 ```
-composer require holt59/cakephp3-bootstrap-helpers:v4.0.0-alpha
+composer require holt59/cakephp3-bootstrap-helpers:dev-v4.0.0-alpha
 ```
 
 **Documentation**