https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS
跨域需要设置服务器端的
Access-Control-Allow-Origin = '*'
The only allowed values for the [Content-Type ](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Type) header are: application/x-www-form-urlencoded multipart/form-data text/plain