docstr: update buffer after learn
          
code: def after_update(self):
      """update buffer after learn"""
      self.share_obs[0] = self.share_obs[-1].copy()
      self.obs[0] = self.obs[-1].copy()
      self.masks[0] = self.masks[-1].copy()
      self.active_masks[0] = self.active_masks[-1].copy()
  
file_path: PARL/benchmark/torch/mappo/mappo_buffer.py
imports: import torch
  import numpy
label_desc: Use image node_id 3 for calling the SeparatedReplayBuffer obj's underlying member method code with example usage: obj.after_update() without return types