Bumped faraday dependency to 0.9.0

According to issue #23, I've bumped faraday dependency to 0.9.0, and run tests. All have passed :) (439 examples, 0 failures, 1 pending).

I've removed ruby-debug dependencies from Gemfile as they are not compatible with any supported Ruby version.

It leads to rather odd case - if you try to run specs on 2.1.0 bundling does not pass as it fails to compile ruby-debug (it is for 1.8.x). On 1.8.7 it fails to bundle, too, as nokogiri no longer supports < 1.9.2.

As ruby-debug was designed to be used only with 1.8.x and it is an obsolete ruby version plus ruby-debug are purely developer dependencies, I've just removed these deps from Gemfile.