Bump chisel3 from `a931c5e2` to `2b977a74` (#311)

Bumps [chisel3](https://github.com/freechipsproject/chisel3) from `a931c5e2` to `2b977a74`.
- [Release notes](https://github.com/freechipsproject/chisel3/releases)
- [Commits](https://github.com/freechipsproject/chisel3/compare/a931c5e218014c659bbff7d0dec74c882281d9a0...2b977a74293a49e9e2a5d960a6a9c07df22430ce

)

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

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