title: autoplot using wrong time for xts
body: <p>I used <code>autoplot()</code> function to plot a time series data including the arima forecast from the <code>forecast()</code> function. The x-axis of the plot is wrong. The data is used xts from 2000/01/01 to 2019/09/01, but obviously the result is not using this time.</p>
  
  <pre><code>fed.arima &lt;- auto.arima(FEDFUNDS_ts)
  fore1 &lt;- forecast(fed.arima,level = c(95),h=12)
  plot(fore1)
  autoplot(fore1)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/6XnRS.png" rel="nofollow noreferrer">plot(fore1)</a></p>
  
  <p><a href="https://i.stack.imgur.com/yNHF8.png" rel="nofollow noreferrer">enter image description here</a></p>