readme: update

Author: dg

readme.md

@@ -26,7 +26,7 @@ The recommended way to install Nette Caching is via Composer:
 composer require nette/caching
 ```
 
-It requires PHP version 5.6 and supports PHP up to 7.3. The dev-master version requires PHP 7.1.
+It requires PHP version 7.1 and supports PHP up to 7.3.
 
 
 Usage