I tried to build it with Mono 5 on Linux, but when running it says that it cannot find "Lidgren.Network".
Also, your build process tries to call "copy" somewhere, which obviously will not work on Linux, but that should not be a big problem. By the way, your own build runs fine even under Mono 4.6.

Unfortunately, I have not much experience with Mono. I will try to setup a clean environment with all dependencies when I have the time.