swift version for simple sprit game according to link below
http://www.raywenderlich.com/zh-hans/51919/sprite-kit-%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B
swift version for simple sprit game according to link below
http://www.raywenderlich.com/zh-hans/51919/sprite-kit-%E5%85%A5%E9%97%A8%E6%95%99%E7%A8%8B