Bump chisel3 from `d8733957` to `ffc4fb5b` (#198)

Bumps [chisel3](https://github.com/freechipsproject/chisel3) from `d8733957` to `ffc4fb5b`.
- [Release notes](https://github.com/freechipsproject/chisel3/releases)
- [Commits](https://github.com/freechipsproject/chisel3/compare/d8733957b584afda3239f239e034b0a7267c0732...ffc4fb5bff3edb6b3bd315cf7e2da91ba12e8b79

)

---
updated-dependencies:
- dependency-name: chisel3
  dependency-type: direct:production
...

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