… This issue stems from having a copy of the expired WWDR Intermediate certificate in both your System and Login keychains. To
resolve the issue,you should first download and install the new WWDR
intermediate certificate (by double-clicking on the file). Next,in
the Keychain Access application,select the System keychain. Make sure
to select “Show Expired Certificates” in the View menu and then delete
the expired version of the Apple Worldwide Developer Relations
Certificate Authority Intermediate certificate (expired on February
14,2016). Your certificates should now appear as valid in Keychain
Access and be available to Xcode for submissions to the App Store.

遵循以下简单步骤：

>从顶部菜单打开钥匙串转到查看>显示过期的证书.
>现在在Keychain中从左侧面板的“登录”选项卡和“系统”选项卡中找到过期的Apple全球开发者关系证书颁发机构,并从两个选项卡中删除它.
>下载证书：https://developer.apple.com/certificationauthority/AppleWWDRCA.cer并双击安装它.>重启Xcode.