Bump firrtl from `264c538` to `899f1f6` (#154)

Bumps [firrtl](https://github.com/freechipsproject/firrtl) from `264c538` to `899f1f6`.
- [Release notes](https://github.com/freechipsproject/firrtl/releases)
- [Commits](https://github.com/freechipsproject/firrtl/compare/264c5380ef390d9e6e3ae619c684453f75951d58...899f1f6efcbd84c0bb9ef0529e024dd36de2bf4f

)

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