message: avoiding double lock
diff: @@ -156,8 +156,10 @@ impl <LB> ResponseCache for Session<LB> where LB: Send {
  return Some(frame);
  }
  - self.responses.lock().await.insert(frame.stream, frame);
  - self.responses.lock().await.remove(&stream_id)
  + let mut responses = self.responses.lock().await;
  +
  + responses.insert(frame.stream, frame);
  + responses.remove(&stream_id)
  }
  }
  