title: Pandas date range does not include the start and end dates
body: <p>I have 2 dates: Nov 1,2018 and Jan 1, 2019.
  I want to generate a monthly date corresponding to the first of every month. I did:</p>
  
  <pre><code>didx=pd.date_range(start='11/01/2018', end='01/01/2019', freq='M',closed=None)
  </code></pre>
  
  <p>But I got:</p>
  
  <pre><code>2018-11-30
  2018-12-31
  </code></pre>
  
  <p>I want:</p>
  
  <pre><code>2018-11-01
  2018-12-01
  2019-01-01
  </code></pre>