It doesn't work. :-) More specifically, it doesn't work because coveralls is trying to use JAXB, which is not available by default in JDK9. (It ships. It's just not available without command line arguments.)
The coveralls plugin is using JAXB for a single static method, to convert a byte[] digest into a hex string. That's such a common form of encoding - if only there was some sort of library to do that. 🤔 PR submitted.
