update Gaudi version to v31r0.002

corresponds to the official v31r0 tag in Gaudi

main changes in this version:

• gaudi/Gaudi!847 (merged) support for LCG_95
• gaudi/Gaudi!788 (merged) change formatting style to clang-format 7
• gaudi/Gaudi!840 (merged) CPUCrunchSvc
• gaudi/Gaudi!831 (merged) EventIDBase and EventIDRange extensions
• gaudi/Gaudi!835 (merged) better debugging of event views and sub slots