title: Why do I get a 'FutureWarning' with pandas.concat?
body: <p>Does anyone meet this similar <code>FutureWarning</code>? I got this when I was using Tiingo+pandas_datareader?</p>
  <p>The warning is like:</p>
  <pre><code>python3.8/site-packages/pandas_datareader/tiingo.py:234: FutureWarning: In a future version of pandas all arguments of concat except for the argument 'objs' will be keyword-only
      return pd.concat(dfs, self._concat_axis)
  </code></pre>
  <p>I think this warning does not impact my accessing to pandas data(in my case, I fetch from tiingo api), I can get all the data I want with no problem.
  I just want to understand if there is any risk with my current enviroment:</p>
  <pre><code>my python3                -  3.8.5, 
  Python 3.8.5, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
  pandas_datareader version -  0.10.0
  pandas version            -  1.3.2
  </code></pre>
  <p>I then tested my code with a 'futureVersion' of python: 3.9.6 (comparing with python 3.8.5). To my suprise, I no longer get any warning or error, everything works fine:</p>
  <p>bellow are details updated</p>
  <pre><code>platform win32 
  - Python 3.9.6, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
  </code></pre>
  <p>Any advice is appreciated.</p>