ISSUE-109: Updated PHP version in README.md

Author: raymondschouten

README.md

@@ -6,7 +6,7 @@
 
 [![Build Status](https://travis-ci.org/darkwebdesign/symfony-addon-constraints.svg?branch=4.0)](https://travis-ci.org/darkwebdesign/symfony-addon-constraints?branch=4.0)
 [![Coverage Status](https://codecov.io/gh/darkwebdesign/symfony-addon-constraints/branch/4.0/graph/badge.svg)](https://codecov.io/gh/darkwebdesign/symfony-addon-constraints)
-[![PHP Version](https://img.shields.io/badge/php-5.5%2B-777BB3.svg)](https://php.net/)
+[![PHP Version](https://img.shields.io/badge/php-7.1%2B-777BB3.svg)](https://php.net/)
 [![Symfony Version](https://img.shields.io/badge/symfony-4.0-93C74B.svg)](https://symfony.com/)
 
 Symfony Add-on Constraints is a collection of extra Symfony validation constraints that you can use in your Symfony