Update qbs submodule.

Contains fixes for the following two bugs uncovered when testing
Creator integration:
    - Qt4/Qt5 incompatibility regarding build graph serialization.
    - Refusal to load stored build graph because the project file
      is wrongly diagnosed to be different from the stored one.

Change-Id: I2466eb1e0751d6309047334daf2d9994dc1bef31
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>