Debugger: Fix debugging with newer Qt Creator's

Make sure we advertise the QDataStream version, so that Qt Creator
doesn't fall back to Qt_4.7.

This is the minimal change necessary to achieve this. QtQml does
actually consider the maximum data version announced on the client side,
but that would require bigger changes in this module ...

Task-number: QTCREATORBUG-10694
Change-Id: I1f0f005429e4d2736dc8661dd8c0d869279f856e
Reviewed-by: Aurindam Jana <aurindam.jana@digia.com>