changed checkstyle version to 6.7 because of incompatibilties with gradle
changed checkstyle version to 6.7 because of incompatibilties with gradle

HyungJon/HubTurbo,ianngiaw/HubTurbo,saav/HubTurbo,Honoo/HubTurbo,Sumei1009/HubTurbo,ianngiaw/HubTurbo,HyungJon/HubTurbo,gaieepo/HubTurbo,saav/HubTurbo,gaieepo/HubTurbo,Honoo/HubTurbo,Sumei1009/HubTurbo