title: openpyxl flip chart with datetime category
body: <p>i want to flip the chart in openpyxl by X axis (originally X axis is ordered from max to min. i want to order from min to max) but</p>
  
  <pre><code>chart.x_axis.scaling.orientation = 'minMax'
  </code></pre>
  
  <p>does not work since my categary is datetime. I cannot change the original data. </p>