cassandra-maven-plugin: CMP-7. Fix group ID for maven-invoker-plugin

issue: https://jira.kiji.org/browse/CMP-7
review: https://review.kiji.org/r/2064
commit: https://github.com/kijiproject/cassandra-maven-plugin/commit/f0c28d2b55545a4ad552f2b59c12c9d6e0b875fd