先将url转成blob类文件对象，在通过a标签的download属性下载，并重命名
仅支持Chrome Firefox
```
var url = 'https://b-gold-cdn.xitu.io/v3/static/img/logo.a7995ad.svg'
var xhr = new XMLHttpRequest();
xhr.open('GET', url, true);
xhr.responseType = 'blob';
xhr.onload = function() {
if (xhr.status === 200) {
var blob = xhr.response
var link = document.createElement('a');
var body = document.querySelector('body');
link.href = window.URL.createObjectURL(blob);
link.download = '测试';
link.style.display = 'none';
body.appendChild(link);
link.click();
body.removeChild(link);
}
};
xhr.send();
```
