title: Cannot load tensorflow_hub
body: <p>after writing import tensorflow_hub, the following error emerges:</p>
  
  <pre><code>class LatestModuleExporter(tf.estimator.Exporter):
  </code></pre>
  
  <p>AttributeError: module 'tensorflow.python.estimator.estimator_lib' has no attribute 'Exporter'</p>
  
  <p>I'm using python 3.6 with tensorflow 1.7 on Windows 10</p>
  
  <p>thanks!</p>