update Rakefile for the new Rubyzip interface and optionally use bundler

Running `rake build` gives an error when using rubyzip > 1 as it has a new interface (see: https://github.com/rubyzip/rubyzip#important-note).

This PR fixes the issue. I also added a Gemfile to use with bundler. That way we can explicitly define the required gem versions if something else changes in the future.

Cheers.