After some trial/error I figured out that babun doesn’t support ruby/gem installed with pact.. So I to fix this I did
Remove the ruby pact packages
pact remove ruby pact remove rubygems
The next commands must be done in the normal windows Command Prompt!
Download the Ruby [Windows-based installer](http://rubyinstaller.org/) (which installs also rubygems), during install choose to add it to PATH, so wehn you run
ruby -v ruby 2.2.3p173 (2015-08-18 revision 51636) [x64-mingw32]
It shows the version number
Add an alias to the new installed gem
Now if you run
gem -v 22.214.171.124
You get the version outputed.
Last step is to install the [Ruby Development-Kit](https://github.com/oneclick/rubyinstaller/wiki/Development-Kit)