v2.7.8

Change log:

b34e555 Upgrade versions; prepare for release
308fbd7 Fix Spring Integration Link in Doc
2bee3ad Fix ConsumerAcknowledgment,toString()
1ebd215 Fix EmbeddedKafkaHolder Example Class Names
838b802 GH-1961: Polishing
ac91313 GH-1961: DefaultDestinationTopicResolver: Inconsistencies In Spring Cloud Environment (#1962)
61ea315 GH-1952: Fix Possible NPE