updated Travis status image

Hi Eric,
in some tests I did it looked like the URL you're using for the Travis image doesn't always get updated. 

Maybe I'm wrong. Just in case you may want to force a build error, see if the image gets updated and get the compilation OK again. Or maybe it's just because the image gets cached by Github for a little while.

If you click in the right side icon in https://travis-ci.org/yosethegame/yosethegame you'll see this is the recommend URL.

Cheers.