bump version to v2.8.0
bump version to v2.8.0

(cherry picked from commit 14af25f1de6832228539259b821949d20069a222)

adamreese/deployment-manager,technosophos/k8s-helm,michelleN/deployment-manager,appscode/helm,SlickNik/helm,bacongobbler/helm,technosophos/deployment-manager,bacongobbler/helm,fibonacci1729/helm,technosophos/k8s-helm,adamreese/helm,michelleN/deployment-manager,technosophos/deployment-manager,helm/helm,michelleN/deployment-manager,adamreese/deployment-manager,eicnix/helm,michelleN/deployment-manager,fibonacci1729/helm,adamreese/deployment-manager,helm/helm,adamreese/helm,technosophos/deployment-manager,eicnix/helm,adamreese/deployment-manager,jascott1/helm,appscode/helm,SlickNik/helm,technosophos/deployment-manager,jascott1/helm,adamreese/deployment-manager,technosophos/deployment-manager