fix #62 Specifying viewBox, width, and height in svg

[vimaxwell]

fix svg with viewBox and width, height in #62

[dnfield]

In local testing using the SVG reported in #62, this makes no visual difference.

[vimaxwell]

@dnfield sorry for late reply.

This is my demo code for rendering svg image .

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      body: Center(
        child: Container(
          color: Colors.blue[200],
          child: SvgPicture.network(
            'https://math.vercel.app/?from=%5Cfrac%7B1%7D%7B%5CGamma%28s%29%7D%5Cint_%7B0%7D%5E%7B%5Cinfty%7D%5Cfrac%7Bu%5E%7Bs-1%7D%7D%7Be%5E%7Bu%7D-1%7D%5Cmathrm%7Bd%7Du.svg',
            placeholderBuilder: (BuildContext context) => Container(
              padding: const EdgeInsets.all(30.0),
              child: const CircularProgressIndicator(),
            ),
          ),
        ),
      ),
    ),
  ));
}

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