message: Switch example to use doctest.
diff: @@ -179,12 +179,14 @@ def _RGBToHSVGrad(op, grad):
  Usage Example:
  - ```python
  - # Decode an image and convert it to HSV.
  - rgb_image = tf.image.decode_png(..., channels=3)
  - rgb_image_float = tf.image.convert_image_dtype(rgb_image, tf.float32)
  - hsv_image = tf.image.rgb_to_hsv(rgb_image)
  - ```
  + >>> rgb_image = tf.stack([
  + ... tf.zeros([5,5]),
  + ... tf.zeros([5,5]),
  + ... tf.ones([5,5])],
  + ... axis=-1)
  + >>> hsv_image = tf.image.rgb_to_hsv(rgb_image)
  + >>> hsv_image[1,1].numpy()
  + array([0.6666667, 1. , 1. ], dtype=float32)
  Args:
  op: The `rgb_to_hsv` `Operation` that we are differentiating.
  