Issue invoke AlpacaPaperTrading

Error calling the [AlpacaPaperTrading ](https://github.com/AI4Finance-Foundation/FinRL/blob/4028be5daf1080300e3f8373427f197b248bed35/finrl/meta/env_stock_trading/env_stock_papertrading.py#L40)
(FinRl/finrl/meta/env_stock_trading/env_stock_papertrading.py)
from
FinRL/examples/FinRL_PaperTrading_Demo.ipynb

>
> ---------------------------------------------------------------------------
>
> ImportError Traceback (most recent call last)
>
> [](https://localhost:8080/#) in
> ----> 1 paper_trading_erl = AlpacaPaperTrading(ticker_list = DOW_30_TICKER,
> 2 time_interval = '1Min',
> 3 drl_lib = 'elegantrl',
> 4 agent = 'ppo',
> 5 cwd = './papertrading_erl_retrain',
>
> [/usr/local/lib/python3.9/dist-packages/finrl/meta/env_stock_trading/env_stock_papertrading.py](https://localhost:8080/#) in __init__(self, ticker_list, time_interval, drl_lib, agent, cwd, net_dim, state_dim, action_dim, API_KEY, API_SECRET, API_BASE_URL, tech_indicator_list, turbulence_thresh, max_stock, latency)
> 38 if drl_lib == "elegantrl":
> 39 from elegantrl.agents import AgentPPO
> ---> 40 from elegantrl.train.run import init_agent
> 41 from elegantrl.train.config import (
> 42 Arguments,
>
> ImportError: cannot import name 'init_agent' from 'elegantrl.train.run' (/usr/local/lib/python3.9/dist-packages/elegantrl/train/run.py)

**To Reproduce**

Run FinRL/examples/FinRL_PaperTrading_Demo.ipynb on Colab

**Expected behavior**
This paper trading demo works pretty smooth without bugs a couple of days ago (Before #915 )

**Screenshots**