function types cannot have argum

从Swift3.0开始, 苹果官方建议方法中函数类型的参数不要带参数名称, 尤其是不能带外部参数名.
参考链接: https://github.com/apple/swift-evolution/blob/master/proposals/0111-remove-arg-label-type-significance.md

func request(urlString: String, parameters: [String : Any], completion: @escaping (result: Any?, Error?) -> ()) {}