Plugin activation not properly configured

I had to do a deep dive with a java debugger on killbill to figure out how this works and what the problem is.

It appears Apache Felix (`org.apache.felix`) uses some metadata/reflection in what seems to be called JNI headers? for the key `Bundle-Activator`.

Killbill uses this as part of its plugin system. If it is missing the plugin does not get properly registered on boot at `src/main/java/org/killbill/billing/payment/provider/DefaultPaymentProviderPluginRegistry.java` (killbill).

So I will be submitting a small PR to fix the `pom.xml`. This requires rebuilding & re-packaging the jar since the metadata is compiled into the jar itself.