Added libsfml to .travis
Added libsfml to .travis

arjanfrans/plane,arjanfrans/plane2d,ArjanFrans/brecourt,ArjanFrans/brecourt,arjanfrans/plane2d,ArjanFrans/brecourt,arjanfrans/plane,arjanfrans/plane,ArjanFrans/brecourt,arjanfrans/plane2d,arjanfrans/plane,arjanfrans/plane2d