vega-embed: Promise is Error in IE11

I use vega and vega-embed.js older version, it work very well.

I update vega to 3.05 and vega-embed to 3.0.0-beta.19, an error happend at line 1196 in 3.0.0-beta.19/vega-embed.js. I found the same error from 3.0.0-beta.19 to 3.0.0-beta.19 22.

function embedMain(el, spec, opt) {
  // Ensure any exceptions will be properly handled
  return new Promise((accept, reject) => {
    embed(el, spec, opt).then(accept, reject);
  });
}