node: update flaming fir (#3508)

* node: reduce block time to 3s and add primary probability constant

* node: update flaming fir chain spec

* node: fix integration test

substrate/node/runtime/src/lib.rs

@@ -563,7 +563,7 @@ impl_runtime_apis! {
 			babe_primitives::BabeConfiguration {
 				median_required_blocks: 1000,
 				slot_duration: Babe::slot_duration(),
-				c: (278, 1000),
+				c: PRIMARY_PROBABILITY,
 			}
 		}