2、合理设置预览消费队列的线程数

Bumps [xstream](https://github.com/x-stream/xstream) from 1.4.6 to 1.4.15.
- [Release notes](https://github.com/x-stream/xstream/releases)
- [Commits](https://github.com/x-stream/xstream/commits)
Signed-off-by: dependabot[bot] <support@github.com>

Merge pull request !19 from zhangxiaoxiao/master

添加QQ群-2群