setup oss.sonatype.org deployment

needed to do the "install gems" differently since it conflicted with
the main artifact.

if snapshot version ```$mvn deploy``` will deploy the artifact to
https://oss.sonatype.org/content/repositories/snapshots/ and the released
version will go to a staging repository on https://oss.sonatype.org/content/repositories/

it is also possible to use the maven release mantra:
* mvn release:prepare
* mvn release:perform