rocksdb requirement should be updated to faust-streaming-rocksdb

[jkgenser]

Checklist

https://github.com/faust-streaming/faust/blob/master/requirements/extras/rocksdb.txt

Steps to reproduce

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Expected behavior

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Actual behavior

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Full traceback

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Versions

• Python version
• Faust version
• Operating system
• Kafka version
• RocksDB version (if applicable)

[taybin]

Fixed by #168