Bump chisel3 from `6a943006` to `4c873b78` (#184)

Bumps [chisel3](https://github.com/freechipsproject/chisel3) from `6a943006` to `4c873b78`.
- [Release notes](https://github.com/freechipsproject/chisel3/releases)
- [Commits](https://github.com/freechipsproject/chisel3/compare/6a943006144c0561daaae28a717440d4a835564c...4c873b78a04967e709e7218ab6bae1390f431da6

)

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

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