Use Scala 2.12 (#167)
Use Scala 2.12 (#167)

Related public PRs:

* https://github.com/apache/kafka/pull/5530
* https://github.com/confluentinc/ksql/pull/2074
* https://github.com/confluentinc/support-metrics-client/pull/54

Tested with muckrake that all projects compile fine if all the PRs are merged.
confluentinc/common,confluentinc/common