Commit 1de6646 removed launch4j from the code and uses maven dependencies instead. Sadly the workdir jars of launch4j 3.4.0 only include the binaries for Windows, not for Linux and OS X.

https://repo.maven.apache.org/maven2/net/sf/launch4j/launch4j/3.4.0/launch4j-3.4.0-workdir-mac.jar
https://repo.maven.apache.org/maven2/net/sf/launch4j/launch4j/3.4.0/launch4j-3.4.0-workdir-linux.jar