看来该方法
stringByAppendingPathComponent已在Swift 2.0中删除，因此错误消息建议使用：
let writePath = NSURL(fileURLWithPath: NSTemporaryDirectory()).URLByAppendingPathComponent("instagram.igo")更新：
URLByAppendingPathComponent()已被替换为
appendingPathComponent()：
let writePath = NSURL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("instagram.igo")
