fix build status icon

Author: ElectricMaxxx

README.md

@@ -1,6 +1,6 @@
 # Symfony Content Management Framework Sandbox  
 
-[![Build Status](https://secure.travis-ci.org/symfony-cmf/cmf-sandbox.png?branch=master)](http://travis-ci.org/symfony-cmf/cmf-sandbox) [![SensioLabsInsight](https://insight.sensiolabs.com/projects/01a6d3b6-a2b4-4a0a-b3cd-2b46a62d6ed9/mini.png)](https://insight.sensiolabs.com/projects/01a6d3b6-a2b4-4a0a-b3cd-2b46a62d6ed9)
+[![Build Status](https://travis-ci.org/symfony-cmf/cmf-sandbox.svg?branch=master)](https://travis-ci.org/symfony-cmf/cmf-sandbox)
 [![StyleCI](https://styleci.io/repos/1316499/shield)](https://styleci.io/repos/1316499)
 [![Dependency Status](https://www.versioneye.com/php/symfony-cmf:sandbox/badge.svg)](https://www.versioneye.com/php/symfony-cmf:sandbox)