Update Rakefile Jeweler to support redis gems > v.2

There are now "redis" gems of 3.0 and up.

In the Rakefile, there is a "pessimistic" dependency on redis 2.2 (~> 2.2), but this conflicts what's listed in the Gemfile (>= 2.2).

So, when doing a bundle install that is grabbing the latest redis (3.0.2), it fails when I go to actually activate the gem.


As the current test suite seems to pass (MRI 1.9.3, OS X 10.8.2), I figured I'd just update the Jeweler spec to match.