Bump firrtl from `d9bdb6a` to `3d12cf4` (#345)

Bumps [firrtl](https://github.com/freechipsproject/firrtl) from `d9bdb6a` to `3d12cf4`.
- [Release notes](https://github.com/freechipsproject/firrtl/releases)
- [Commits](https://github.com/freechipsproject/firrtl/compare/d9bdb6af20934c296196ec074ad819f51da04311...3d12cf4165f7851ff838467b1e5ab36592ae4fcb

)

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

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