Update hello-world-plugin

[Neal Fultz]

I have been trying to learn how to work with plugins by modifying the hello-world-plugin linked from the wiki to work with Jobs DSL, and encountered lots of maven issues. 

I sent a PR to the github repo to update it enough to fix my problems, but if someone is really knowledgeable about pom.xml it could use a second pair of eyes, especially since the tutorial/wiki hadn't been updated in so long.

Thanks much,

Neal