由于原版的html2canvas在对跨域图片获取上总是失败的问题，将跨域改为通过GM_xmlhttpRequest获取
This script should not be not be installed directly. It is a library for other scripts to include with the meta directive // @require https://update.greatest.deepsurf.us/scripts/456607/1143054/GM_html2canvas.js
# 我的设置如下
let options = {
allowTaint: true,
logging: true,
useCORS: true,
}
html2canvas(document.documentElement, options ).then( canvas =>{
var base64Image = canvas.toDataURL("image/png");
})