Use subclasses for contracts rather than fully converting Swagger to Legacy contracts.
Rename native -> legacy, because I plan to drop support eventually
Implement and add contract tests to both subclasses, using rspec shared examples
I think 20 lines is still pretty readable
Fix SwaggerContract and use :legacy instead of :default
Fix goliath so the server only runs once (also testing travis hook)
Fix WebMock issue reported in #158