Bump chisel3 from `ffc086e3` to `af2cd8e6` (#150)

Bumps [chisel3](https://github.com/freechipsproject/chisel3) from `ffc086e3` to `af2cd8e6`.
- [Release notes](https://github.com/freechipsproject/chisel3/releases)
- [Commits](https://github.com/freechipsproject/chisel3/compare/ffc086e373f3583a5399b46ecfcd41cd88dc9beb...af2cd8e6e03da14442fca7e84e97767ad3242187

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