documentation issue

Hej there - I just tried to follow the installation instructions of **platform-samples/api/ruby/find-inactive-members/** and the command
gem install octokit
does not work. I tried it with the regular admin, as well as with elevated rights (sudo). The error message is the same:
-bash: gem: command not found

Start with the installation instructions for platform-samples/api/ruby/find-inactive-members/ and reproduce the reported `gem install octokit` command. The current failure is `-bash: gem: command not found`; done means the instructions provide a working path for installing the dependency or clearly document the required prerequisite.

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