Unexpected keyword argument 'json' when using webhook

[deviantony]

When trying to use the webhook with the latest version of the tool, the following exception is raised:

ERROR:xtrabackup.full_backup:pyxtrabackup failed.
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/xtrabackup/full_backup.py", line 55, in main
    arguments['--webhook'])
  File "/usr/local/lib/python2.7/dist-packages/xtrabackup/backup_tools.py", line 216, in start_full_backup
    self.trigger_webhook(webhook)
  File "/usr/local/lib/python2.7/dist-packages/xtrabackup/backup_tools.py", line 162, in trigger_webhook
    self.http.post(webhook_url, postdata)
  File "/usr/local/lib/python2.7/dist-packages/xtrabackup/http_manager.py", line 7, in post
    requests.post(url, json=json)
  File "/usr/lib/python2.7/dist-packages/requests/api.py", line 88, in post
    return request('post', url, data=data, **kwargs)
  File "/usr/lib/python2.7/dist-packages/requests/api.py", line 44, in request
    return session.request(method=method, url=url, **kwargs)
TypeError: request() got an unexpected keyword argument 'json'