message: doctests fix ubuntu cpu test fail
diff: @@ -1868,10 +1868,10 @@ def rgb_to_grayscale(images, name=None):
  pixels.
  ```python
  - >>> original = tf.constant([[[1.0], [2.0], [3.0]]])
  + >>> original = tf.constant([[[1.0, 2.0, 3.0]]])
  >>> converted = tf.image.rgb_to_grayscale(original)
  >>> print(converted.shape)
  - (1, 3, 3)
  + (1, 1, 1)
  ```
  Args:
  @@ -1905,10 +1905,10 @@ def grayscale_to_rgb(images, name=None):
  The input images' last dimension must be size 1.
  ```python
  - >>> original = tf.constant([[[1.0, 2.0, 3.0]]])
  + >>> original = tf.constant([[[1.0], [2.0], [3.0]]])
  >>> converted = tf.image.grayscale_to_rgb(original)
  >>> print(converted.shape)
  - (1, 1, 1)
  + (1, 3, 3)
  ```
  Args:
  