Fix token economics url. (#4355)

* Fix token economics url.

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/frame/staking/src/lib.rs

@@ -173,7 +173,7 @@
 //! calculated using the era duration and the staking rate (the total amount of tokens staked by
 //! nominators and validators, divided by the total token supply). It aims to incentivise toward a
 //! defined staking rate. The full specification can be found
-//! [here](https://research.web3.foundation/en/latest/polkadot/Token%20Economics/#inflation-model).
+//! [here](https://research.web3.foundation/en/latest/polkadot/Token%20Economics.html#inflation-model).
 //!
 //! Total reward is split among validators and their nominators depending on the number of points
 //! they received during the era. Points are added to a validator using