title: Getting "NameError: name 'Reduction' is not defined" error in Tensorflow 1.13
body: <p>I am trying to use def 'tf.losses.mean_squared_error'. But I am getting </p>
  
  <pre><code>NameError: name 'Reduction' is not defined
  </code></pre>
  
  <p>I am using TF 1.13. 
  Is that some import issue or has there been any update in the tf.losses.mean_squared_error function?</p>
  
  <p>My code is as follows.</p>
  
  <pre><code>def reg_loss(pred, GT):
      loss = tf.losses.mean_squared_error(
      labels = GT,
      predictions = pred,
      weights=1.0,
      scope=None,
      loss_collection=tf.GraphKeys.LOSSES,
      reduction=Reduction.SUM_BY_NONZERO_WEIGHTS)
  
      return reg_loss
  </code></pre>
  
  <p>Could anyone please help me resolve this issue?</p>