title: Problem converting Keras model to Tensorflow-Lite using TocoConverter.from_keras_model_file
body: <p>I'm facing an issue using TOCO to convert a Keras model to TfLite.  </p>
  
  <p>Followed the guide of: <a href="https://www.tensorflow.org/api_docs/python/tf/contrib/lite/TocoConverter" rel="nofollow noreferrer">https://www.tensorflow.org/api_docs/python/tf/contrib/lite/TocoConverter</a></p>
  
  <p>How I use TOCO:</p>
  
  <pre><code>def create_lite_model(keras_model_file):
      lite_model_name = 'lite_model_file.tflite'
      tf_lite_graph = os.path.join(WEIGHTS_DIRECTORY, lite_model_name)
      converter = tf.contrib.lite.TocoConverter.from_keras_model_file(keras_model_file)
      tf_lite_model = converter.convert()
      open(tf_lite_graph, "wb").write(tf_lite_model)
  </code></pre>
  
  <p>Getting the following error:</p>
  
  <pre><code>File "/tensorflow/contrib/lite/python/lite.py", line 356, in from_keras_model_file
  keras_model = _keras.models.load_model(model_file)
  File "/tensorflow/python/keras/engine/saving.py", line 251, in load_model
  training_config['weighted_metrics'])
  KeyError: 'weighted_metrics'
  </code></pre>
  
  <p>Does anybody has a solution for this problem?</p>