We should upgrade to Spark 2.2.0 to stay current. However, Spark 2.2 has dropped support for Java 7. (See more details in the release notes here and the jira SPARK-19493)
As discussed on the dev mailing list (here) we should upgrade and document that the Spark 2 modules require JDK 8. Additionally we will need to use JDK 8 when running the Jenkins build.