title: FutureWarning: In a future version of pandas all arguments of concat except for the argument 'objs'
body: <p>I am getting this warning while using add_constant method from sm.</p>
  <pre><code>sm.add_constant(data)
  </code></pre>
  <p>can anyone help me to resolve this</p>
  <p>/opt/conda/lib/python3.7/site-packages/statsmodels/tsa/tsatools.py:142: FutureWarning: In a future version of pandas all arguments of concat except for the argument 'objs' will be keyword-only
  x = pd.concat(x[::order], 1)</p>