add a current_epoch to BabeApi (#7789)

* add a `current_epoch` to BabeApi

* add current_epoch_start back again

* fix node-runtime

* bump spec version

substrate/bin/node/runtime/src/lib.rs

@@ -111,7 +111,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// and set impl_version to 0. If only runtime
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
-	spec_version: 260,
+	spec_version: 261,
 	impl_version: 0,
 	apis: RUNTIME_API_VERSIONS,
 	transaction_version: 2,
@@ -1141,6 +1141,10 @@ impl_runtime_apis! {
 			Babe::current_epoch_start()
 		}
 
+		fn current_epoch() -> sp_consensus_babe::Epoch {
+			Babe::current_epoch()
+		}
+
 		fn generate_key_ownership_proof(
 			_slot_number: sp_consensus_babe::SlotNumber,
 			authority_id: sp_consensus_babe::AuthorityId,