Add poser badges

Author: marcospassos

README.md

@@ -1,6 +1,7 @@
 # ANTLR4 Runtime for PHP
 [![Travis CI](https://api.travis-ci.org/antlr/antlr-php-runtime.svg?branch=master)](https://travis-ci.org/antlr/antlr-php-runtime)
-[![BSD-3-Clause](https://img.shields.io/badge/license-BSD3-brightgreen.svg)](https://github.com/antlr/antlr-php-runtime/blob/master/LICENSE)
+[![Latest Stable Version](https://poser.pugx.org/antlr/antlr4-php-runtime/v/stable)](https://packagist.org/packages/antlr/antlr4-php-runtime)
+[![License](https://poser.pugx.org/antlr/antlr4-php-runtime/license)](https://packagist.org/packages/antlr/antlr4-php-runtime)
 
 ### First steps