`aws-sdk` has been updated to support newer version of nokogiri, so we
should loosen our dependency.

Needs work for S3 Attachments.

This is necessary so Gemnesium will be green.

The original commit came from @amazonwebservices and @trevorrowe in #579.
I had to revise the commit and make sure all the test cases are passing.
All credits still goes to those guys, thanks a lot!

This also removes Pry.

This test will generate a basic Rails application, include Paperclip
into Gemfile, and call basic `has_attached_file` in the model. This will
make sure that we're not messing up any of the configuration and
integration for our gem and the Rails framework.

Closes #507

(cherry picked from commit e053805f55b872e6926dfbfa14f38d1296e8b922)