when doing `lein run` avoid that ClassNotFoundException: ships.core
without this, only lein uberjar (and maybe also lein jar) would compile
ships.core into a .class; lein compile or lein javac or lein run
wouldn't

tested with lein 2.2.0
Merge pull request #3 from AtKaaZ/avoidClassNotFoundException

when doing `lein run` avoid that ClassNotFoundException: ships.core