pay out slashes to the treasury (#3446)

substrate/node/runtime/src/lib.rs

@@ -237,8 +237,8 @@ impl staking::Trait for Runtime {
 	type CurrencyToVote = CurrencyToVoteHandler;
 	type OnRewardMinted = Treasury;
 	type Event = Event;
-	type Slash = ();
-	type Reward = ();
+	type Slash = Treasury; // send the slashed funds to the treasury.
+	type Reward = (); // rewards are minted from the void
 	type SessionsPerEra = SessionsPerEra;
 	type BondingDuration = BondingDuration;
 	type SessionInterface = Self;