Upgrades for library compatibility

This pull request includes a few changes:

i) Eliminating use of the now removed should_change macro in the tests
ii) Updating the use of FactoryGirl to use the new syntax rather than the older syntax that is not supported in the latest versions of the FactoryGirl gem
iii) Editing the gemspec to support Rails versions greater than 3.0.x
iv) Adding a .travis.yml file

It would be great if this could be pulled in and a new gem version released.  I'm looking to use this gem on a new Rails 3.2 project.

Please let me know if there's anything else I can do to make that happen.  Thanks.