Bump treadle from `1d6fdbc` to `31867cb` (#127)

Bumps [treadle](https://github.com/freechipsproject/treadle) from `1d6fdbc` to `31867cb`.
- [Release notes](https://github.com/freechipsproject/treadle/releases)
- [Commits](https://github.com/freechipsproject/treadle/compare/1d6fdbcc7df804872dda602da38d68fe5e0717c4...31867cbce25a53c25b2d2a8639e1696121c391c9

)

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