Update qbs submodule.

This updates qbs to the HEAD of the 1.1 bugfix branch, which has
a number of bug fixes on top of what's in the RC.

Change-Id: I95e3c8b45befb639c4a016b32cbe88145baae16f
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

qbs @ 3b6b1b7f

-Subproject commit acddeb82e5df0d8f947c3e02f5da64a351855023
+Subproject commit 3b6b1b7fbc50bca101ad89a8acd80774bc668dde