造成 Provisional headers are shown

1. 跨域使用了json

  // 后端设置http头部, 允许跨域使用json数据格式
  ctx.set("Content-Type", "application/json;charset=utf-8");
  ctx.set('Access-Control-Allow-Origin','*')
  ctx.set("Access-Control-Allow-Headers",  " Origin, X-Requested-With, Content-Type, Accept");