message: fix: use const instead of let.
diff: @@ -340,7 +340,7 @@ class SVGPainter implements PainterBase {
  this._oldVNode = null;
  }
  toDataURL(base64?: boolean) {
  - let str = encodeURIComponent(this.renderToString());
  + const str = encodeURIComponent(this.renderToString());
  return 'data:image/svg+xml;'
  + (base64 ? 'base64,' + encodeBase64(str) : 'charset=UTF-8,' + str);
  }
  