Bump firrtl from `7ceebcf` to `4d6cf34` (#164)

Bumps [firrtl](https://github.com/freechipsproject/firrtl) from `7ceebcf` to `4d6cf34`.
- [Release notes](https://github.com/freechipsproject/firrtl/releases)
- [Commits](https://github.com/freechipsproject/firrtl/compare/7ceebcfffd1bbd823681217ee8629080bd03c79b...4d6cf3425ed214becc895f5771e03c4cc52b95e2

)

---
updated-dependencies:
- dependency-name: firrtl
  dependency-type: direct:production
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>