Fixing rspec test, new Active Support convert_value method signature and version bump

The signature of the method HashWithIndifferentAccess#convert_value has changed in ActiveSupport 4.0.2: http://apidock.com/rails/v4.0.2/ActiveSupport/HashWithIndifferentAccess/convert_value

I also need to use and_call_original to make the test pass on spec/rconfig_spec.rb