doc: Update slashing block downtime number (#7374)

Fixes this issue: #7356

packages/docs/celo-codebase/protocol/proof-of-stake/penalties.md

@@ -27,7 +27,7 @@ Provable slashing conditions cannot be initiated automatically on chain but info
 
 In exchange for sending a transaction which initiates a successful provable slashing condition on-chain, the reporter receives a "reward", a portion of the slashed amount (which will always be greater than the gas costs of the proof). The reward is added to the reporter's balance of non-voting LockedGold. The remainder of the slashed amount is sent to the [Community Fund](community-fund.md).
 
-- **Persistent downtime -** A validator which can be shown to be absent from 5760 consecutive BLS signatures will be slashed 100 CELO, have future rewards suppressed, and (most importantly in this case) will be ejected from its current group.
+- **Persistent downtime -** A validator which can be shown to be absent from 8640 consecutive BLS signatures will be slashed 100 CELO, have future rewards suppressed, and (most importantly in this case) will be ejected from its current group.
 
 - **Double Signing -** A validator which can be shown to have produced BLS signatures for 2 distinct blocks at the same height and in the same consensus round but with different hashes will be slashed 9000 CELO, have future rewards suppressed, and will be ejected from its current group. Note that unlike some proof-of-stake networks, Celo does not penalize validators for double signing regular consensus messages. In particular, one side-effect of how Celo provides liveness can result in cases where honest validators may legitimately double sign blocks across different rounds at the same height (Cosmos terms this [amnesia](https://github.com/tendermint/spec/blob/fa3430ad163a2a0ed77aa3f624a70cd9b8b84b78/spec/consensus/signing.md#other-rules) and also specifically excludes it from slashing).