Update multiple-gpus-concise.md

[XihWang]

因为d2l中的Resudual类已经更改为lazyconv2d，仅需要3个参数，而不是4个，此页的pytorch版本代码会出错。可以见d2l的源码:https://github.com/d2l-ai/d2l-en/blob/master/d2l/torch.py#L581 该链接中的Residual类的定义的一部分如下
class Residual(nn.Module):
"""The Residual block of ResNet models.

Defined in :numref:`sec_resnet`"""
def __init__(self, num_channels, use_1x1conv=False, strides=1):
    super().__init__()
    self.conv1 = nn.LazyConv2d(num_channels, kernel_size=3, padding=1,
                               stride=strides)
    self.conv2 = nn.LazyConv2d(num_channels, kernel_size=3, padding=1)
    if use_1x1conv:
        self.conv3 = nn.LazyConv2d(num_channels, kernel_size=1,
                                   stride=strides)
    else:
        self.conv3 = None
    self.bn1 = nn.LazyBatchNorm2d()
    self.bn2 = nn.LazyBatchNorm2d()

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