安卓手机运行download方法，加上header: { "Content-Type": "multipart/form-data" },后台报错“the request was rejected because no multipart boundary was found”；不加header时报错“the request doesn't contain a multipart/form-data or multipart/mixed stream, content type header is application/x-www-form-urlencoded”。在小程序开发工具和ios上没出现这个问题。