NSData dataWithBytes: 在swift3中的写法

Objective-C用Byte数组来构造一个NSData实例：

    Byte signkey[] = {0x1e,0xc3,0xf8,0x5c,0xb2,0xf2,0x13,0x70,0x26,0x4e,0xb3,0x71,0xc8,0xc6,0x5c,0xa3,0x7f,0xa3,0x3b,0x9d,0xef,0xef,0x2a,0x85,0xe0,0xc8,0x99,0xae,0x82,0xc0,0xf6,0xf8};
    NSData *appSign = [NSData dataWithBytes:signkey length:32];

在swift3中，应该这么写：

let signkey: [UInt8] = [0x1e,0xc3,0xf8,0x5c,0xb2,0xf2,0x13,0x70,0x26,0x4e,0xb3,0x71,0xc8,0xc6,0x5c,0xa3,0x7f,0xa3,0x3b,0x9d,0xef,0xef,0x2a,0x85,0xe0,0xc8,0x99,0xae,0x82,0xc0,0xf6,0xf8]
let appSign: NSData = NSData.init(bytes: signkey, length: 32)

注意，Byte数组在swift中应该声明为[UInt8]，类型如果不显式指定，编译器并不会报错，但是得到的NSData就不对了！