[Bug] DAggerValue, ppo_buffer adds next_obs instead of current_obs

[Phimos]

# Record the transition
self.storage.add_transitions(current_obs, actions_expert, rews, dones)
current_obs.copy_(next_obs)

# value_net
if self.apply_value_net:
    self.ppo_buffer.add_transitions(
        current_obs, current_states, actions, rews, 
        dones, values, actions_log_prob, mu, sigma,
    )
    current_states.copy_(next_states)

the current_obs variable updates before adding transitions to ppo_buffer, so the ppo_buffer actually adds the next_obs instead the current_obs.