update changelog for 2.2.0 release (engine-2.2)
update changelog for 2.2.0 release (engine-2.2)


Former-commit-id: f08b9da8559605f9b75984eb37f34398083deb36
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine