HOW_TO_UPDATE_API_VERSION

As of the 0.9 release, the "build" step is no longer needed. Technically, it never was, but I didn't realize that until now. :-P

When RightMedia updates their release (say, from 1.33 to 1.34), do this:
- Edit the API_VERSION file to match the new release
- Visit the main API doc page (https://api.yieldmanager.com/doc/) and make sure the AVAILABLE_SERVICES file exactly matches the services listed in the sidebar.
- Run all the specs using 'rake' to ensure nothing broke
- Commit/push changes and confirm Travis builds on all rubies we support
- Bump the VERSION in lib/yieldmanager/version.rb appropriately
- 'rake release' to cut a version and push to rubygems.org

And you're done!