Use Scala 2.12 builds of Kafka

Scala versions usually bring some performance improvements. Closes ches#38

Author: ches

CHANGELOG.md

@@ -4,6 +4,7 @@ Release Notes
 ## latest - Unreleased
 
 - Update to Kafka 0.10.2.0 ([bgaechter], #39)
+- Switch to Scala 2.12 builds as now recommended by Kafka.
 - Change config var `GROUP_MAX_SESSION_TIMEOUT_MS` to
   `KAFKA_GROUP_MAX_SESSION_TIMEOUT_MS` for consistency.
 - Allow configuration of `auto.create.topics.enable`,

Dockerfile

@@ -10,7 +10,7 @@ FROM netflixoss/java:8
 MAINTAINER Ches Martin <ches@whiskeyandgrits.net>
 
 # The Scala 2.11 build is currently recommended by the project.
-ENV KAFKA_VERSION=0.10.2.0 KAFKA_SCALA_VERSION=2.11 JMX_PORT=7203
+ENV KAFKA_VERSION=0.10.2.0 KAFKA_SCALA_VERSION=2.12 JMX_PORT=7203
 ENV KAFKA_RELEASE_ARCHIVE kafka_${KAFKA_SCALA_VERSION}-${KAFKA_VERSION}.tgz
 
 RUN mkdir /kafka /data /logs