WKWebView: build fail for iOS 10.2. XCode9 beta 6

We have previously used UIWebView, but since it is now marked as deprecated and is now available to be added to storyboard, we decided to use WKWebView, however when we use WKWebView, we are getting the following error:

error: Class Unavailable: WKWebView before iOS 11.0 (NSCoding support was broken in previous versions)

Once we change the target to iOS11 the build is successful. On Apple site it says that WKWebView should be used since iOS8.

Any help appreciated.

Thanks!