title: AttributeError: 'module' object has no attribute 'NASCell'
body: <p>Pretty much self-explanatory: I would like to use the <a href="https://www.tensorflow.org/versions/master/api_docs/python/tf/contrib/rnn/NASCell" rel="nofollow noreferrer">NASCell</a> in my RNN model, however this line:</p>
  
  <pre><code>nas_cell = tf.contrib.rnn.NASCell(n_input)
  </code></pre>
  
  <p>throws:</p>
  
  <pre><code>AttributeError: 'module' object has no attribute 'NASCell'
  </code></pre>
  
  <p>Where is <code>NASCell</code> located? </p>