title: pyldavis AttributeError: 'DataFrame' object has no attribute 'ix'
body: <p>Im getting this error when I try to run</p>
  <p><code>vis = pyLDAvis.gensim.prepare(lda_model, corpus, dictionary=lda_model.id2word)</code></p>
  <p><code>vis</code>.</p>
  <pre><code>    385    # reorder all data based on new ordering of topics
      386    topic_freq       = topic_freq[topic_order]
  --&gt; 387    topic_term_dists = topic_term_dists.ix[topic_order]
      388    doc_topic_dists  = doc_topic_dists[topic_order]
      
  AttributeError: 'DataFrame' object has no attribute 'ix'
  
  It seems to be an issue with pyLDAvis and pandas
  pyLDAvis 2.1.1
  pandas 1.1.3
  </code></pre>