Use recent Ruby on OSX too
Use recent Ruby on OSX too

The Linux images get Ruby 2.2.4 via the Docker image at
https://github.com/aptible/aptible-omnibus-builder, but the OSX build
happens without Docker and uses Ruby 2.0, which doesn't work with newer
Omnibus and its dependencies.

This fixes that.

aptible/omnibus-aptible-toolbelt,aptible/omnibus-aptible-toolbelt,aptible/omnibus-aptible-toolbelt