message: add newline after doctest expected return
diff: @@ -1872,6 +1872,7 @@ def rgb_to_grayscale(images, name=None):
  >>> converted = tf.image.rgb_to_grayscale(original)
  >>> print(converted.numpy())
  [[[1.8149]]]
  +
  ```
  Args:
  @@ -1911,6 +1912,7 @@ def grayscale_to_rgb(images, name=None):
  [[[1., 1., 1.],
  [2., 2., 2.],
  [3., 3., 3.]]]
  +
  ```
  Args:
  