adjust readme

Author: dbu

README.md

@@ -24,8 +24,8 @@ controller for redirection routes.
 
 ## Requirements
 
-* PHP 7.1 / 7.2
-* Symfony 2.8 / 3.3 / 3.4 / 4.0
+* PHP 7.1 / 7.2 / 7.3 / 7.4
+* Symfony 3.4 / 4.3 / 4.4
 * See also the `require` section of [composer.json](composer.json)
 
 ## Documentation