build: bump gdbstub from 0.6.0 to 0.6.1

Bumps [gdbstub](https://github.com/daniel5151/gdbstub) from 0.6.0 to 0.6.1.
- [Release notes](https://github.com/daniel5151/gdbstub/releases)
- [Changelog](https://github.com/daniel5151/gdbstub/blob/master/CHANGELOG.md)
- [Commits](https://github.com/daniel5151/gdbstub/compare/0.6.0...0.6.1)

---
updated-dependencies:
- dependency-name: gdbstub
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

vmm/Cargo.toml

@@ -25,7 +25,7 @@ clap = "3.1.2"
 devices = { path = "../devices" }
 epoll = "4.3.1"
 event_monitor = { path = "../event_monitor" }
-gdbstub = "0.6.0"
+gdbstub = "0.6.1"
 gdbstub_arch = "0.2.0"
 hypervisor = { path = "../hypervisor" }
 lazy_static = "1.4.0"