My current project in Swift 3.2 and Xcode 8.3 this error comes today even I have successfully uploaded to iTunes before 3 days.
ERROR ITMS-90725: "SDK Version Issue. This app was built with the iOS '10.3' SDK. All new iOS apps submitted to the App Store must be built with the iOS '11.0' SDK or later, included in Xcode [9.0] or later. Please update Xcode and rebuild your app."
From Apple's Submitting apps to the App Store:
Starting April 2018, all new iOS apps submitted to the App Store must be built with the iOS 11 SDK.
And a related (older but probably useful) Technical Note:
It is not practical for Xcode to force every project to build with the latest SDK. For example, it may be necessary to ship an immediate hot-fix version of app - without waiting until the app has been fully updated for a newer SDK.
But it's important to understand that using an older SDK is a temporary workaround, not a solution. Issues preventing your app from using the latest SDK should be fixed as soon as possible. It will be much easier to fix these issues while the older build system is still supported.
Important: No Legacy SDK version will be supported indefinitely.