iOS9 http请求

https://developer.apple.com/library/prerelease/ios/releasenotes/General/WhatsNewIniOS/Articles/iOS9.html#//apple_ref/doc/uid/TP40016198-DontLinkElementID_13在iOS9 beta1中，苹果将原http协议改成了https协议，使用 TLS1.2 SSL加密请求数据。解决办法：在info.plist中添加NSAppTransportSecurityNSAllowsArbitraryLoads