bump php version

README.md

@@ -62,7 +62,7 @@ can also add your own there if you publish one.
 
 ### Requirements
 
-- Monolog 2.x works with PHP 7.1 or above, use Monolog `^1.0` for PHP 5.3+ support.
+- Monolog 2.x works with PHP 7.2 or above, use Monolog `^1.0` for PHP 5.3+ support.
 
 ### Submitting bugs and feature requests