Switch badges to vector in README

Low-res raster makes eyes bleed on retina displays 😎

[skip ci]

README.md

@@ -3,7 +3,7 @@
 [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/Houdini/two_factor_authentication?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 [![Build Status](https://travis-ci.org/Houdini/two_factor_authentication.svg?branch=master)](https://travis-ci.org/Houdini/two_factor_authentication)
-[![Code Climate](https://codeclimate.com/github/Houdini/two_factor_authentication.png)](https://codeclimate.com/github/Houdini/two_factor_authentication)
+[![Code Climate](https://codeclimate.com/github/Houdini/two_factor_authentication.svg)](https://codeclimate.com/github/Houdini/two_factor_authentication)
 
 ## Features