message: Doc: Update example for current version
diff: @@ -1344,21 +1344,19 @@ def cast(x, dtype):
  Returns:
  Keras tensor with dtype `dtype`.
  - Example:
  + Examples:
  + Cast a float32 variable to a float64 tensor
  +
  ```python
  - >>> from keras import backend as K
  - >>> input = K.placeholder((2, 3), dtype='float32')
  - >>> input
  - <tf.Tensor 'Placeholder_2:0' shape=(2, 3) dtype=float32>
  - # It doesn't work in-place as below.
  - >>> K.cast(input, dtype='float16')
  - <tf.Tensor 'Cast_1:0' shape=(2, 3) dtype=float16>
  - >>> input
  - <tf.Tensor 'Placeholder_2:0' shape=(2, 3) dtype=float32>
  - # you need to assign it.
  - >>> input = K.cast(input, dtype='float16')
  - >>> input
  - <tf.Tensor 'Cast_2:0' shape=(2, 3) dtype=float16>
  + >>> import tensorflow as tf
  + >>> from tensorflow.keras import backend as K
  + >>> input = K.ones(shape=(1,3))
  + >>> print(input)
  + >>> cast_input = K.cast(input, dtype='float64')
  + >>> print(cast_input)
  +
  + <tf.Variable 'Variable:0' shape=(1, 3) dtype=float32, numpy=array([[1., 1., 1.]], dtype=float32)>
  + tf.Tensor([[1. 1. 1.]], shape=(1, 3), dtype=float64)
  ```
  """
  return math_ops.cast(x, dtype)
  