docs: def comment(self, issue, body):
          """Comment on existing issue on Github.
          For JSON data returned by Github refer:
          https://developer.github.com/v3/issues/comments/#create-a-comment
  
          :param issue: object of exisiting issue
          :param body: body of the comment
          :returns: dict of JSON data returned by Github of the new comment
          :rtype: `dict`
  
          """
          url = issue.comments_url
          data = {'body': body}
  
          response = self.session.post(url, json.dumps(data))
          assert response.status_code == 201
  
          return json.loads(response.content)