Upgrade Ruby to 2.1
Add Connection#cancel

- Changed Api::Response to handle optional and fewer fields
- Tested both failure response and success for #cancel
- Add cancellation path to Circle CI environment
- Add cancel path environment variable to Travis
- Remove redundant connection_v03 spec
Move Connection#post and #cancel fully into shared examples
- Use do…end or single line let statements with curly braces
Make method names internally consistent

Rename valid_failure_response to post_failed_response_body to be consistent with cancel_failed_response_body.
Merge pull request #23 from Curatur/cancel_request

Allow user to cancel API processing