Bump firrtl from `4d6cf34` to `270c913` (#165)

Bumps [firrtl](https://github.com/freechipsproject/firrtl) from `4d6cf34` to `270c913`.
- [Release notes](https://github.com/freechipsproject/firrtl/releases)
- [Commits](https://github.com/freechipsproject/firrtl/compare/4d6cf3425ed214becc895f5771e03c4cc52b95e2...270c91380d8d7c0c2fe3583b65450500d49845b6

)

---
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>