node: update flaming fir (#3681)

* node: reduce grandpa justification period to 512 blocks

* node: update flaming fir chainspec

substrate/node-template/src/service.rs

@@ -134,7 +134,7 @@ pub fn new_full<C: Send + Default + 'static>(config: Configuration<C, GenesisCon
 	let grandpa_config = grandpa::Config {
 		// FIXME #1578 make this available through chainspec
 		gossip_duration: Duration::from_millis(333),
-		justification_period: 4096,
+		justification_period: 512,
 		name: Some(name),
 		keystore: Some(service.keystore()),
 	};