use oss.s.o maven repository in order to get sync to central

Pull request to make POM changes needed to deploy to oss.sonatype.org which will sync to maven central.

See the [singup docs](https://docs.sonatype.org/display/Repository/Sonatype+OSS+Maven+Repository+Usage+Guide#SonatypeOSSMavenRepositoryUsageGuide-2.Signup) for the final steps to get perms to push, etc.