Added activesupport as a dependency

In Rails 3.2.12 I got the following error:

    Bundler could not find compatible versions for gem "activesupport":
      In Gemfile:
        feedzirra (= 0.1.3) ruby depends on
          activesupport (~> 3.1.1) ruby

        rails (~> 3.2.12) ruby depends on
          activesupport (3.2.12)