Since Qt installers nowadays (since Qt 5.3) register all Qt patch
releases of the same minor version with the same ID, the Kit will not be
updated (because the Qt 'is the same'), so it should use %{Qt:Version}
instead of hardcoding the version.

Change-Id: Ieb8b766490b3c6297fa11802c6e13724658795d5
Task-number: QTCREATORBUG-15128
Reviewed-by: Tobias Hunger <tobias.hunger@theqtcompany.com>