Change build status badge to 2.4.x branch

Author: AkenRoberts

README.md

@@ -1,6 +1,6 @@
 # Doctrine Behavioral Extensions
 
-[![Build Status](https://secure.travis-ci.org/Atlantic18/DoctrineExtensions.png)](http://travis-ci.org/Atlantic18/DoctrineExtensions)
+[![Build Status](https://travis-ci.org/Atlantic18/DoctrineExtensions.svg?branch=v2.4.x)](https://travis-ci.org/Atlantic18/DoctrineExtensions)
 [![Latest Stable Version](https://poser.pugx.org/gedmo/doctrine-extensions/version)](https://packagist.org/packages/gedmo/doctrine-extensions)
 
 This package contains extensions for Doctrine ORM and MongoDB ODM that offer new functionality or tools to use Doctrine