Locking down a specific version of rubyzip

The 1.0.0 version of rubyzip changes that API in a way that breaks
our code. We should change our code to work with the latest API.
Bumping the version number and cleaning up the gemspec

The gemspec referred to the VERSION file which hasn't been updated
in a long, long time. That is now gone.

The gemspec has been bumped in anticpiation of a new release.
Date TBD.