message: Fix documentation in `tf.keras.layers.Add` example
  This fixes
  (https://www.tensorflow.org/api_docs/python/tf/keras/layers/Add#class_add)
diff: @@ -235,9 +235,7 @@ class Add(_Merge):
  x1 = keras.layers.Dense(8, activation='relu')(input1)
  input2 = keras.layers.Input(shape=(32,))
  x2 = keras.layers.Dense(8, activation='relu')(input2)
  - added = keras.layers.Add()([x1, x2]) # equivalent to added =
  - keras.layers.add([x1, x2])
  -
  + added = keras.layers.Add()([x1, x2]) # equivalent to added = keras.layers.add([x1, x2])
  out = keras.layers.Dense(4)(added)
  model = keras.models.Model(inputs=[input1, input2], outputs=out)
  ```
  