[Run2_2017] Update the CMSSW version
Created by: aperloff
Change the CMSSW version to CMSSW_10_2_21. This change works as confirmed by a fresh checkout of the software and two unit tests.
Created by: aperloff
Change the CMSSW version to CMSSW_10_2_21. This change works as confirmed by a fresh checkout of the software and two unit tests.