Configure shadowJar classifier in time for packageNative config
Configure shadowJar classifier in time for packageNative config

This change avoids the "Main application jar is missing" error described
in the comments on issue #243.

bisq-network/exchange,ManfredKarrer/exchange,myteer/bitsquare,metabit/bitsquare,sakazz/exchange,bisq-network/exchange,haiqu/bitsquare,bitsquare/bitsquare,bitsquare/bitsquare,myteer/bitsquare,ManfredKarrer/exchange,sakazz/exchange,haiqu/bitsquare,metabit/bitsquare