Replace append dataframe by concat

[bangyuwen]

Traceback (most recent call last):
  File "/Users/bangyuwen/Documents/Github/crypto-analysis/strategies/test.py", line 5, in <module>
    ohlcv = finlab_crypto.crawler.get_all_binance("BTCUSDT", "4h")
  File "/Users/bangyuwen/Documents/Github/crypto-analysis/.venv/lib/python3.10/site-packages/finlab_crypto/crawler.py", line 89, in get_all_binance
    data_df = data_df.append(temp_df)
  File "/Users/bangyuwen/Documents/Github/crypto-analysis/.venv/lib/python3.10/site-packages/pandas/core/generic.py", line 5989, in __getattr__
    return object.__getattribute__(self, name)
AttributeError: 'DataFrame' object has no attribute 'append'. Did you mean: '_append'?