UIWebview未覆盖顶部状态栏

隐藏导航栏，UIWebview未覆盖顶部状态栏

解决方法：

if (@available(iOS 11.0, *)) {
        self.webView.scrollView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
    } else {
        self.edgesForExtendedLayout = UIRectEdgeNone;
    }