text: Title: JSONDecoderError
  Body: Hi, 
  
  I'm trying to run with the vectorbt example with the following packages
  
  ```sh
  Package Versions:
  Numpy v1.20.1
  Pandas v1.2.3
  vectorbt >= v0.18.1
  ```
  
  Pandas TA v0.2.75b0
  To install the Latest Version:
  ```sh
  $ pip install -U git+https://github.com/twopirllc/pandas-ta
  ```
  
  When I tried
  
  ```python
  benchmarks = dl(benchmark_tickers, lc_cols=True)
  ```
  
  I got
  ```sh
  JSONDecodeError                           Traceback (most recent call last)
  <ipython-input-6-1a9746513a1f> in <module>
  ----> 1 benchmarks = dl(benchmark_tickers, lc_cols=True)
  
  <ipython-input-3-8955b4500e88> in dl(tickers, same_start, **kwargs)
       44         _df = pd.DataFrame()
       45         for ticker in tickers:
  ---> 46             received[ticker] = _df.ta.ticker(ticker, **kwargs)
       47             print(f"[+] {ticker}{received[ticker].shape} {ta.get_time(full=False, to_string=True)}")
       48 
  
  c:\source\pandas-ta-master\pandas-ta-master\pandas_ta\core.py in ticker(self, ticker, **kwargs)
      836         ds = ds.lower() is not None and isinstance(ds, str)
      837         # df = av(ticker, **kwargs) if ds and ds == "av" else yf(ticker, **kwargs)
  --> 838         df = yf(ticker, **kwargs)
      839 
      840         if df is None: return
  
  c:\source\pandas-ta-master\pandas-ta-master\pandas_ta\utils\_data.py in yf(ticker, **kwargs)
      124         # Ticker Info & Chart History
      125         yfd = yfra.Ticker(ticker)
  --> 126         df = yfd.history(period=period, interval=interval, proxy=proxy, **kwargs)
      127 
      128         if df.empty: return
  
  ~\miniconda3\envs\vectorbt\lib\site-packages\yfinance\base.py in history(self, period, interval, start, end, prepost, actions, auto_adjust, back_adjust, proxy, rounding, tz, **kwargs)
      154                                "Our engineers are working quickly to resolve "
      155                                "the issue. Thank you for your patience.")
  --> 156         data = data.json()
      157 
      158         # Work with errors
  
  ~\miniconda3\envs\vectorbt\lib\site-packages\requests\models.py in json(self, **kwargs)
      898                     # used.
      899                     pass
  --> 900         return complexjson.loads(self.text, **kwargs)
      901 
      902     @property
  
  ~\miniconda3\envs\vectorbt\lib\json\__init__.py in loads(s, cls, object_hook, parse_float, parse_int, parse_constant, object_pairs_hook, **kw)
      355             parse_int is None and parse_float is None and
      356             parse_constant is None and object_pairs_hook is None and not kw):
  --> 357         return _default_decoder.decode(s)
      358     if cls is None:
      359         cls = JSONDecoder
  
  ~\miniconda3\envs\vectorbt\lib\json\decoder.py in decode(self, s, _w)
      335 
      336         """
  --> 337         obj, end = self.raw_decode(s, idx=_w(s, 0).end())
      338         end = _w(s, end).end()
      339         if end != len(s):
  
  ~\miniconda3\envs\vectorbt\lib\json\decoder.py in raw_decode(self, s, idx)
      353             obj, end = self.scan_once(s, idx)
      354         except StopIteration as err:
  --> 355             raise JSONDecodeError("Expecting value", s, err.value) from None
      356         return obj, end
  
  JSONDecodeError: Expecting value: line 1 column 1 (char 0)
  ```
  
  Any ideas?
  
  Thanks.
  
  