GenericToolbox.Root.h ROOT_VERSION fix needed

[JacekHoleczek]

The cpp-generic-toolbox/include/GenericToolbox.Root.h file contains:

#if ROOT_VERSION_CODE >= ROOT_VERSION(6,28,04)
    return gDirectory.fValue->load();
#elif ROOT_VERSION_CODE >= ROOT_VERSION(6,23,02)
    return gDirectory.fValue.load();
#else

I do not know which ROOT versions allow "gDirectory.fValue.load()" but the "operator->" is also needed for "ROOT_VERSION(6,26,14)" (I do not have here any previous ROOT versions to test it further, sorry).

[nadrino]

It could that the 6.28 was chosen as it was installed on my computer and figured out there was a problem with this particular version.

Perhaps we could find the exact version where the -> is required