Update Gemfile for new version of rubyzip

Adjust the Gemfile so people can use `bundle install` for the albacore dependency.

According to the [rubyzip README](https://github.com/rubyzip/rubyzip#important-note), the Rubyzip interface has changed, and the appropriate way to specify the dependency in a Gemfile is:

    gem 'rubyzip', '>= 1.0.0' # will load new rubyzip version
    gem 'zip-zip' # will load compatibility for old rubyzip API.