使用tableview内嵌wkwebview，获取webview的高度不正确，底部出现一大片空白
NSString *jScript = @"var meta = document.createElement('meta'); meta.setAttribute('name', 'viewport'); meta.setAttribute('content', 'width=device-width,user-scalable=no'); document.getElementsByTagName('head')[0].appendChild(meta);";
WKUserScript *wkUScript =[[WKUserScript alloc] initWithSource: jScript injectionTime:WKUserScriptInjectionTimeAtDocumentEnd forMainFrameOnly:YES];
WKUserContentController *wkUController = [[WKUserContentController alloc] init];
[wkUController addUserScript:wkUScript];
改变html页头，不能缩放
