title: Pandas interpolate throws an invalid fill method error after version 0.24
body: <p>The <code>pandas.DataFrame.interpolate()</code> method is throwing this error when using the <code>method='time'</code> argument:</p>
  
  <pre class="lang-sh prettyprint-override"><code>Error: Invalid fill method. Expecting pad (ffill) or backfill (bfill). Got time
  </code></pre>
  
  <p>This only started happening after <code>pandas</code> updated to version 0.24, which seems to have changed some implementation. Code that used to work breads with version 0.24 or greater.</p>
  
  <p>I thought it might have to do with the data types of the columns, meaning that if the <code>DataFrame</code> included non-numeric columns the interpolation would fail. That doesn't seems to be the case though, since I've recently run into this again with a purely numeric <code>DataFrame</code>.</p>
  
  <p>I believe I got this to work at some point, but I can't remember how (other than messing with data types). This is problematic because my existing codebase has to pin pandas to 0.23 for the functionality to work.</p>