Update readme (use SVG build badges)

Author: iMattPro

README.md

@@ -2,7 +2,7 @@
 
 An extension for phpBB 3.1 that allows administrators to easily add their Google Analytics tracking code to their phpBB forum.
 
-[![Build Status](https://travis-ci.org/phpbb-extensions/googleanalytics.png)](https://travis-ci.org/phpbb-extensions/googleanalytics)
+[![Build Status](https://travis-ci.org/phpbb-extensions/googleanalytics.svg)](https://travis-ci.org/phpbb-extensions/googleanalytics)
 [![Scrutinizer Code Quality](https://scrutinizer-ci.com/g/phpbb-extensions/googleanalytics/badges/quality-score.png?b=master)](https://scrutinizer-ci.com/g/phpbb-extensions/googleanalytics/?branch=master)
 
 ## Install