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>