It looks like test runs started failing when Travis CI updated their default workers to Xenial and switched from the Oracle JVM to OpenJDK.
Example failure: https://travis-ci.org/edx/jenkins-job-dsl/builds/570887129
Example success: https://travis-ci.org/edx/jenkins-job-dsl/builds/562693178
This might be fixed easily via a Gradle upgrade or such.