title: tensorflow_core._api.v2.random has no attribute Generator
body: <p>I am seeing the following error when I try to import <code>tensorflow_addons</code> with tensorflow 2.1</p>
  <pre><code>&gt; import tensorflow_addons as tfa
  AttributeError: module 'tensorflow_core._api.v2.random' has no attribute 'Generator'
  </code></pre>