升级Swift4.0扫描二维码不回调

代理AVCaptureMetadataOutputObjectsDelegate的回调函数已被重命名：

所以，替换

func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!)

至

func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection)