UIWebview的内存泄露问题导致我彻底的抛弃了他，该用WkWebview
通过注入js的方式，可以实现scalesPageToFit属性效果
代码如下:
NSString *jScript = @"var meta = document.createElement('meta'); meta.setAttribute('name', 'viewport'); meta.setAttribute('content', 'width=device-width'); document.getElementsByTagName('head')[0].appendChild(meta);";
WKUserScript *wkUScript = [[WKUserScript alloc] initWithSource:jScript injectionTime:WKUserScriptInjectionTimeAtDocumentEnd forMainFrameOnly:YES];
WKUserContentController *wkUController = [[WKUserContentController alloc] init];
[wkUController addUserScript:wkUScript];
WKWebViewConfiguration *wkWebConfig = [[WKWebViewConfiguration alloc] init];
wkWebConfig.userContentController = wkUController;
WKWebView *contentWebView = [[WKWebView alloc] initWithFrame:CGRectZero configuration:wkWebConfig];
