fix bug (conv2d groups: 'num_channels % groups is not 0:' )

[chengduoZH]

        if num_channels % groups is not 0:
            raise ValueError("num_channels must be divisible by groups.")
        num_filter_channels = num_channels / groups

This expression( if num_channels % groups is not 0) is wrong, it should be if num_channels % groups != 0

[JiayiFeng]

LGTM