code: public Response deleteAfterDays(String bucket, String key, int days) throws QiniuException {
          return rsPost(bucket, String.format("/deleteAfterDays/%s/%d", encodedEntry(bucket, key), days), null);
      }
docs: 设置文件的存活时间
  
  @param bucket 空间名称
  @param key    文件名称
  @param days   存活时间，单位：天