Update slashing.rs
Link was a dead-end
//! has multiple misbehaviors. However, accounting for such cases is necessary
//! to deter a class of "rage-quit" attacks.
//!
-//! Based on research at <https://research.web3.foundation/en/latest/polkadot/slashing/npos/>
+//! Based on research at <https://w3f-research.readthedocs.io/en/latest/polkadot/slashing/npos.html>
use super::{
EraIndex, Config, Module, Store, BalanceOf, Exposure, Perbill, SessionInterface,
