message: Update TFL style transfer doc to use TF Hub model
diff: "content_path = tf.keras.utils.get_file('belfry.jpg','https://storage.googleapis.com/khanhlvg-public.appspot.com/arbitrary-style-transfer/belfry-2611573_1280.jpg')\n",
  "style_path = tf.keras.utils.get_file('style23.jpg','https://storage.googleapis.com/khanhlvg-public.appspot.com/arbitrary-style-transfer/style23.jpg')\n",
  "\n",
  - "style_predict_path = tf.keras.utils.get_file('style_predict.tflite', 'https://storage.googleapis.com/download.tensorflow.org/models/tflite/arbitrary_style_transfer/style_predict_quantized_256.tflite')\n",
  - "style_transform_path = tf.keras.utils.get_file('style_transform.tflite', 'https://storage.googleapis.com/download.tensorflow.org/models/tflite/arbitrary_style_transfer/style_transfer_quantized_384.tflite')"
  + "style_predict_path = tf.keras.utils.get_file('style_predict.tflite', 'https://tfhub.dev/google/lite-model/magenta/arbitrary-image-stylization-v1-256/int8/prediction/1?lite-format=tflite')\n",
  + "style_transform_path = tf.keras.utils.get_file('style_transform.tflite', 'https://tfhub.dev/google/lite-model/magenta/arbitrary-image-stylization-v1-256/int8/transfer/1?lite-format=tflite')"
  ]
  },
  {
  },
  "name": "Artistic Style Transfer with TensorFlow Lite.ipynb",
  "private_outputs": true,
  - "provenance": []
  + "provenance": [],
  + "toc_visible": true
  },
  "kernelspec": {
  - "display_name": "Python 2",
  - "name": "python2"
  + "display_name": "Python 3",
  + "name": "python3"
  }
  },
  "nbformat": 4,
  