r20: Bump github.com/hashicorp/yamux from 0.1.1 to 0.1.2

Bumps [github.com/hashicorp/yamux](https://github.com/hashicorp/yamux) from 0.1.1 to 0.1.2.
- [Release notes](https://github.com/hashicorp/yamux/releases)
- [Commits](https://github.com/hashicorp/yamux/compare/v0.1.1...v0.1.2)

---
updated-dependencies:
- dependency-name: github.com/hashicorp/yamux
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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