message: refact huber loss
diff: @@ -1445,14 +1445,12 @@ def huber(y_true, y_pred, delta=1.0):
  delta = math_ops.cast(delta, dtype=K.floatx())
  error = math_ops.subtract(y_pred, y_true)
  abs_error = math_ops.abs(error)
  - quadratic = math_ops.minimum(abs_error, delta)
  - linear = math_ops.subtract(abs_error, quadratic)
  + half = ops.convert_to_tensor_v2(0.5, dtype=abs_error.dtype)
  return K.mean(
  - math_ops.add(
  - math_ops.multiply(
  - ops.convert_to_tensor_v2(0.5, dtype=quadratic.dtype),
  - math_ops.multiply(quadratic, quadratic)),
  - math_ops.multiply(delta, linear)),
  + array_ops.where_v2(
  + abs_error <= delta,
  + half * math_ops.pow(error, 2),
  + half * math_ops.pow(delta, 2) + delta * (abs_error - delta)),
  axis=-1)
  