kiji-mapreduce: KIJIMR-294. Add group ID to maven-archetype-plugin.

issue: https://jira.kiji.org/browse/KIJIMR-294
review: https://review.kiji.org/r/2062
commit: https://github.com/kijiproject/kiji-mapreduce/commit/52398463b7c6de8ed3029da4eaaa5cb80226e95e