fix provisioner metric docs (#4359)

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

node/core/provisioner/src/metrics.rs

@@ -23,9 +23,9 @@ struct MetricsInner {
 	request_inherent_data: prometheus::Histogram,
 	provisionable_data: prometheus::Histogram,
 
-	/// The dispute_statement.* metrics trak how many disputes/votes the runtime will have to process. It will count
+	/// The `dispute_statement_*` metrics track how many disputes/votes the runtime will have to process. It will count
 	/// all recent statements meaning every dispute from last sessions: 10 min on Rococo, 60 min on Kusama and
-	/// 4 hours on Polkadot. The metrics are updated only when the node authors block, so values vary across nodes.
+	/// 4 hours on Polkadot. The metrics are updated only when the node authors a block, so values vary across nodes.
 	dispute_statement_sets_requested: prometheus::Counter<prometheus::U64>,
 	dispute_statements_requested: prometheus::CounterVec<prometheus::U64>,
 }