root,roofit: bump version

New hash: 5b99d2b619e3f1a0dc8b8fef7b7b626728aba3d6

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge branch 'IB/CMSSW_7_1_X/root6' of github.com:cms-sw/cmsdist into IB/CMSSW_7_1_X/root6