title: flag provided but not defined: --mount
body: <p>I'm pretty new with Tensorflow Serving, and I followed the basic instruction from: <a href="https://tensorflow.google.cn/serving/serving_basic" rel="nofollow noreferrer">https://tensorflow.google.cn/serving/serving_basic</a></p>
  
  <p>All previous steps are ok, but when I use:</p>
  
  <p>docker run -p 8500:8500 --mount type=bind,source=/tmp/mnist,target=/models/mnist -e MODEL_NAME=mnist -t tensorflow/serving &amp;</p>
  
  <p>It gave me:
  flag provided but not defined: --mount</p>
  
  <p>Can someone help me with it?</p>