Allow both minor and patch changes in dependencies

The optimistic operator `~>` is tricky. I only recently learned how it works. The level of precision determines what ranges are allowed (http://guides.rubygems.org/patterns/).

With the current gemspec `rubyzip` and `htmlentities` are pinned down to only path level changes. This change allows `rubyzip >= 1.1 && < 2.0` which is fine.

Only allowing patch level changes causes needless dependency issues.

This adjustment is theoretically safe as long as semantic versioning is adhered to by the dependencies.