May I ask you why you are not installing the rubyzip gem directly from rubygems as it suggests ?
Is there a specific reason why you are trying to install from source ? If not, then I would suggest you to take the approach recommended by the gem itself, and install it from rubygems using a command like gem install rubyzip. If for some reason you wish to install the latest from source, I would suggest you to contact the developer or check the source directly…