苹果官网的提示
Thanks for bringing this to the attention of the community and apologies for the issues you’ve been having. 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.

• Download https://developer.apple.com/certificationauthority/AppleWWDRCA.cer
• Double-click to install to Keychain.
• Then in Keychain, Select View -> “Show Expired Certificates” in Keychain app.
• It will list all the expired certifcates.
• Delete “Apple Worldwide Developer Relations Certificate Authority certificates” from “login” tab
• And also delete it from “System” tab.
  Now you are ready go.