Update pet_sprites.css

Added missing wolf base position.

Same deal as the mount request. New sprite sheet image is attached here:
![pet_sprites](https://f.cloud.github.com/assets/2374703/304043/fe8af654-9633-11e2-99f3-1766faf79dbb.png)

Can either take this request or wait for one tonight that includes the png within the request.

Wolf was just tacked onto the end of image and CSS for ease. May rearrange in the future.

!Untested!