Update parity-scale-codec to 2.0 (#7994)

* update cargo.toml

* use 2.0 in mmmr

substrate/primitives/finality-grandpa/src/lib.rs

@@ -102,7 +102,7 @@ pub enum ConsensusLog<N: Codec> {
 	/// This should be a pure function: i.e. as long as the runtime can interpret
 	/// the digest type it should return the same result regardless of the current
 	/// state.
-	#[codec(index = "1")]
+	#[codec(index = 1)]
 	ScheduledChange(ScheduledChange<N>),
 	/// Force an authority set change.
 	///
@@ -118,18 +118,18 @@ pub enum ConsensusLog<N: Codec> {
 	/// This should be a pure function: i.e. as long as the runtime can interpret
 	/// the digest type it should return the same result regardless of the current
 	/// state.
-	#[codec(index = "2")]
+	#[codec(index = 2)]
 	ForcedChange(N, ScheduledChange<N>),
 	/// Note that the authority with given index is disabled until the next change.
-	#[codec(index = "3")]
+	#[codec(index = 3)]
 	OnDisabled(AuthorityIndex),
 	/// A signal to pause the current authority set after the given delay.
 	/// After finalizing the block at _delay_ the authorities should stop voting.
-	#[codec(index = "4")]
+	#[codec(index = 4)]
 	Pause(N),
 	/// A signal to resume the current authority set after the given delay.
 	/// After authoring the block at _delay_ the authorities should resume voting.
-	#[codec(index = "5")]
+	#[codec(index = 5)]
 	Resume(N),
 }