Missing 64-bit support issue on app update

My app is on appstore, on submitting new version to store we are getting mail from app store team.

Dear developer,
We have discovered one or more issues with your recent delivery for "app name". Your delivery was successful, but you may wish to correct the following issues in your next delivery:
Missing 64-bit support - Beginning on February 1, 2015 new iOS apps submitted to the App Store must include 64-bit support and be built with the iOS 8 SDK. Beginning June 1, 2015 app updates will also need to follow the same requirements. 
To enable 64-bit in your project, we recommend using the default Xcode build setting of “Standard architectures” to build a single binary with both 32-bit and 64-bit code. 

We are using "Standard architectures" and tested it on both 32 and 64 bit actual devices(iPhone 5 and iPhone 6 and more), and app running fine.

Please anyone let me know where I am wrong, why I am getting this.