Fix nar-download in multi-module builds

In my multi-module aggregator-based build, I have a shared library NAR.

I would like to incorporate it into one of the other modules (an RPM) by using the nar-download goal.

However, this does not work correctly because nar-download looks for the JAR + NAR in the local repository (rather than in the module's target directory).

I am not certain that this is a universally correct fix, but it does work for me.