message: Make SoftplusGrad convertible
diff: @@ -2010,6 +2010,7 @@ def _convert_biasaddgrad(pfor_input):
  @RegisterPForWithArgs("ReluGrad")
  @RegisterPForWithArgs("TanhGrad")
  @RegisterPForWithArgs("SigmoidGrad")
  +@RegisterPForWithArgs("SoftplusGrad")
  def _convert_grads(pfor_input, op_type, *args, **kw_args):
  del args
  del kw_args
  