Add version badge

Author: ddeboer

README.md

@@ -3,6 +3,7 @@ FOSHttpCache
 [![Build Status](https://travis-ci.org/FriendsOfSymfony/FOSHttpCache.svg?branch=master)](https://travis-ci.org/FriendsOfSymfony/FOSHttpCache) 
 [![Scrutinizer Quality Score](https://scrutinizer-ci.com/g/FriendsOfSymfony/FOSHttpCache/badges/quality-score.png?s=bc263d4deb45becdb1469b71e8630c5e65efdcf4)](https://scrutinizer-ci.com/g/FriendsOfSymfony/FOSHttpCache/) 
 [![Code Coverage](https://scrutinizer-ci.com/g/FriendsOfSymfony/FOSHttpCache/badges/coverage.png?s=a19df7bb7e830642fb937891aebe8c3e1c9f59c0)](https://scrutinizer-ci.com/g/FriendsOfSymfony/FOSHttpCache/)
+[![Latest Stable Version](https://poser.pugx.org/friendsofsymfony/http-cache/v/stable.svg)](https://packagist.org/packages/friendsofsymfony/http-cache)
 
 Introduction
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