Allow Faraday 0.9 to satisfy dependency.

There's no difference between using Faraday 0.8 and Faraday 0.9 for this project. Both work correctly as far as I can see.

I needed to loosen the Gemspec requirements to be able to include the gem into a number of projects - so here's a PR that loosens it to be either 0.8 or 0.9.