Rbx

Looks like after fixing the installation problem there was another different and unrelated problem envolving Rubinius.

Ever since updating to v2 Rubinius has been nothing but a pain.

Other's experiencing similar problems:
https://github.com/puma/puma/issues/382

Looks like it was fixed in an updated version:
https://github.com/rubysl/rubysl-json/issues/1

Anyway, this should fix it and even if it doesn't I've allowed rbx's failure for now.