Update statistics of episode after each step

def on_step_end(self, step, logs):
        """ Update statistics of episode after each step """
        episode = logs['episode']
        self.observations[episode].append(logs['observation'])
        self.rewards[episode].append(logs['reward'])
        self.actions[episode].append(logs['action'])
        self.metrics[episode].append(logs['metrics'])
        self.step += 1