Hashie compatibility for both 3.1 and <3.1

- Use exception catching to handle compatibility. I tried respond_to and private_methods.include?, but exception catching seems to be the most accurate
- Add a hashie gemfile for tests pre and post 3.1 changes (copy of rails32)
- Disable rbx-19 in travis because travis doesn't seem to support it anymore
- Disable 1.8.7 + Rails 4 build because Rails doesn't support 1.8.7
- Add a compatibility check to gemspec because Hashie 3.1 doesn't support 1.8.7