message: doctests update
  print converted.numpy() instead of shape for rgb_to_grayscale and grayscale_to_rgb
diff: @@ -1870,8 +1870,8 @@ def rgb_to_grayscale(images, name=None):
  ```python
  >>> original = tf.constant([[[1.0, 2.0, 3.0]]])
  >>> converted = tf.image.rgb_to_grayscale(original)
  - >>> print(converted.shape)
  - (1, 1, 1)
  + >>> print(converted.numpy())
  + array([[[1.8149]]], dtype=float32)
  ```
  Args:
  @@ -1907,8 +1907,10 @@ def grayscale_to_rgb(images, name=None):
  ```python
  >>> original = tf.constant([[[1.0], [2.0], [3.0]]])
  >>> converted = tf.image.grayscale_to_rgb(original)
  - >>> print(converted.shape)
  - (1, 3, 3)
  + >>> print(converted.numpy())
  + array([[[1., 1., 1.],
  + [2., 2., 2.],
  + [3., 3., 3.]]], dtype=float32)
  ```
  Args:
  