message: Fix the variable typo in the python api example
diff: @@ -28,7 +28,7 @@ val = img + tf.constant([1., 2., 3.]) + tf.constant([1., 4., 4.])
  out = tf.identity(val, name="out")
  with tf.Session() as sess:
  tflite_model = tf.contrib.lite.toco_convert(sess.graph_def, [img], [out])
  - open("test.tflite", "wb").write(tflite_modeL)
  + open("test.tflite", "wb").write(tflite_model)
  ```
  **NOTE** Currently, the TOCO command will cause a fatal error to the Python
  