Error ValueError: You are trying to merge on object and datetime64[ns, America/New_York] columns. in processor_yahoofinance.py

**Describe the bug**

Error in processor_yahoofinance.py, def add_technical_indicator

ValueError: You are trying to merge on object and datetime64[ns, America/New_York] columns. If you wish to proceed you should use pd.concat

File "/workspace/FinRL/finrl/train.py", line 110, in
train(
File "/workspace/FinRL/finrl/train.py", line 33, in train
data = dp.add_technical_indicator(data, technical_indicator_list)
File "/home/user/anaconda3/envs/FinRL/lib/python3.9/site-packages/finrl/meta/data_processor.py", line 52, in add_technical_indicator
df = self.processor.add_technical_indicator(df, tech_indicator_list)
**File "/home/user/anaconda3/envs/FinRL/lib/python3.9/site-packages/finrl/meta/data_processors/processor_yahoofinance.py", line 253, in add_technical_indicator
df = df.merge(**
File "/home/user/anaconda3/envs/FinRL/lib/python3.9/site-packages/pandas/core/frame.py", line 10093, in merge
return merge(
File "/home/user/anaconda3/envs/FinRL/lib/python3.9/site-packages/pandas/core/reshape/merge.py", line 110, in merge
op = _MergeOperation(
File "/home/user/anaconda3/envs/FinRL/lib/python3.9/site-packages/pandas/core/reshape/merge.py", line 707, in __init__
self._maybe_coerce_merge_keys()
File "/home/user/anaconda3/envs/FinRL/lib/python3.9/site-packages/pandas/core/reshape/merge.py", line 1346, in _maybe_coerce_merge_keys
raise ValueError(msg)
**ValueError: You are trying to merge on object and datetime64[ns, America/New_York] columns. If you wish to proceed you should use pd.concat**

**To Reproduce**
Steps to reproduce the behavior:
1. Run main.py or train.py from finrl folder. After the data is downloaded, error in data processor, adding indicators.

**Expected behavior**
main or train.py to run without error.

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