Don't include target/ directory element on output tar

I see that the generated archive contained all jar files under a `lib/target/` directory.

I think it'd be better to chop 'target/' off, so the jar files end up under `lib/`. This is my intention with this patch.

Now, this might break some people's existing scripts... So, if you agree on accepting this change, we'd have to bump the minor version number and add a notice about this change on the README.

Thanks!