Update an existing issue on Github.
        For JSON data returned by Github refer:
        https://developer.github.com/v3/issues/#edit-an-issue

        :param issue: object existing issue
        :returns: dict of JSON data returned by Github.
        :rtype: `dict`

def update(self, issue, **kwargs):
        """Update an existing issue on Github.
        For JSON data returned by Github refer:
        https://developer.github.com/v3/issues/#edit-an-issue

        :param issue: object existing issue
        :returns: dict of JSON data returned by Github.
        :rtype: `dict`

        """
        url = issue.url

        response = self.session.patch(url, json.dumps(kwargs))

        assert response.status_code == 200
        return json.loads(response.content)