Cross-publish jackson-module-scala for Scala 2.12

In order to build Spark against Scala 2.12, we need to either remove our jackson-module-scala dependency or cross-publish Jackson for Scala 2.12. Personally, I'd prefer to remove it because I don't think we make extensive use of it and because I'm not a huge fan of the implicit mapping between case classes and JSON wire formats (the extra verbosity required by other approaches is a feature, IMO, rather than a bug because it makes it much harder to accidentally break wire compatibility).