job.cancel() doesn't work - v2 api returns a 405 (Method not allowed)

The API docs for job canellation say that a PUT is needed:

https://app.zencoder.com/docs/api/jobs/cancel

Might that be why the following code gets a 405? That shouldn't be a GET.

core.py:303-308

```
def cancel(self, job_id):
    """
    Cancels a job
    """
    data = {'api_key': self.api_key}
    return self.get(self.base_url + '/%s/cancel' % str(job_id), data=data)
```
