It seems, that libressl removed a few functions used in iojs-v2.0.0. Version 1.6.2 works fine. I haven't test other versions.
See this output for more info:
https://gist.github.com/4199d35343200e58a5d7
System: VoidLinux
Linux: 4.0.1
LibreSSL: 2.1.6_3
io.js: 2.0.0