Prevent PNG Sprite from being downloaded if SVG is supported

![screen shot 2014-06-05 at 17 25 40](https://cloud.githubusercontent.com/assets/85783/3190422/65d60f6e-ecce-11e3-9dde-1bcb379a9e1c.PNG)

![ ](https://github.com/aFarkas/html5shiv/commits/master)