Ignoring return value of function declared with warn_unused_result attribute

[solar555]

Google出了解决方案：
将以下两个方法：
SecRandomCopyBytes(kSecRandomDefault, keyBytes.length, keyBytes.mutableBytes);
SecRandomCopyBytes(kSecRandomDefault, sizeof(uint32_t), (uint8_t *)mask_key);
前添加（void）即可：
(void)SecRandomCopyBytes(kSecRandomDefault, keyBytes.length, keyBytes.mutableBytes);
(void)SecRandomCopyBytes(kSecRandomDefault, sizeof(uint32_t), (uint8_t *)mask_key);
注：可能是因为Xcode8.0 beta的问题，估计Facebook过段时间会解决