Update http://doc.qt.io/qt-5/ios-support.html

http://doc.qt.io/qt-5/ios-support.html says:
"Note: As required by Apple, you should always use the latest Xcode 5 version when building your applications for the App Store. In practice this means you need OS X 10.8 or 10.9 to do iOS development with Qt, as those are the only platforms where Xcode 5 will run."

The Xcode version should be updated to Xcode 6, which is the one we have support for Qt 5.5. Also the OS X version should be updated in that doc.