async function toPNG (page, svg) {
  await page.setContent(`<!DOCTYPE html>  
<html>
<head>  
<meta name="viewport" content="initial-scale=1.0, user-scalable=no" />  
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />  
</head>  
<body> 
${svg}
</body>
</html>`)
  const container = await page.$('svg')
  return Buffer.from(await container.screenshot({
    type: 'png',
    omitBackground: true
  }))
}
@param {Page} page
@param {string} svg
@returns {Promise<Buffer>}