Render a Tropo object into a Json string.

def RenderJson(self, pretty=False):
        """
        Render a Tropo object into a Json string.
        """
        steps = self._steps
        topdict = {}
        topdict['tropo'] = steps
        if pretty:
            try:
                json = jsonlib.dumps(topdict, indent=4, sort_keys=False)
            except TypeError:
                json = jsonlib.dumps(topdict)
        else:
            json = jsonlib.dumps(topdict)
        return json