title: change tf.contrib.layers.xavier_initializer() to 2.0.0
body: <p>how can I change</p>
  <pre><code>tf.contrib.layers.xavier_initializer()
  </code></pre>
  <p>to tf version &gt;= 2.0.0 ??</p>
  <p>all codes:</p>
  <pre><code>W1 = tf.get_variable(&quot;W1&quot;, shape=[self.input_size, h_size],
                               initializer=tf.contrib.layers.xavier_initializer())
  </code></pre>