Use storage_root of newly calculated header (#2216)

Instead of calculating the `storage_root` a second time, we just can
take the `storage_root` from the new header.

substrate/node/runtime/src/lib.rs

@@ -60,7 +60,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	impl_name: create_runtime_str!("substrate-node"),
 	authoring_version: 10,
 	spec_version: 57,
-	impl_version: 58,
+	impl_version: 59,
 	apis: RUNTIME_API_VERSIONS,
 };