LGAlertView 遮罩背景是黑色的隐藏后屏幕全是黑的

https://github.com/Friend-LGA/LGAlertView/issues/69

+ (UIWindow *)appWindow {
    return [UIApplication sharedApplication].windows[0];
}

替换成

+ (UIWindow *)appWindow {
    return [UIApplication sharedApplication].delegate.window;
}