Add a method to fetch current finalized head hash (#57)

* chore: Update to latest substrate master renames

* feat: Introduce Client::finalized_head

src/rpc.rs

@@ -168,6 +168,13 @@ impl<T: System> Rpc<T> {
             })
     }
 
+    /// Get a block hash of the latest finalized block
+    pub fn finalized_head(&self) -> impl Future<Item = T::Hash, Error = Error> {
+        self.chain
+            .finalized_head()
+            .map_err(Into::into)
+    }
+
     /// Get a Block
     pub fn block(
         &self,
@@ -286,7 +293,7 @@ impl<T: System + Balances + 'static> Rpc<T> {
                                 TransactionStatus::Future
                                 | TransactionStatus::Ready
                                 | TransactionStatus::Broadcast(_) => None,
-                                TransactionStatus::Finalized(block_hash) => {
+                                TransactionStatus::InBlock(block_hash) => {
                                     Some(Ok(block_hash))
                                 }
                                 TransactionStatus::Usurped(_) => {