Use storage_root of newly calculated header (paritytech#2216)

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

Author: bkchr

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,
 };
 

srml/executive/src/lib.rs

@@ -23,7 +23,7 @@ use rstd::marker::PhantomData;
 use rstd::result;
 use primitives::traits::{
 	self, Header, Zero, One, Checkable, Applyable, CheckEqual, OnFinalize,
-	OnInitialize, Hash, As, Digest, NumberFor, Block as BlockT, OffchainWorker
+	OnInitialize, As, Digest, NumberFor, Block as BlockT, OffchainWorker
 };
 use srml_support::{Dispatchable, traits::MakePayment};
 use parity_codec::{Codec, Encode};
@@ -238,9 +238,9 @@ impl<
 		}
 
 		// check storage root.
-		let storage_root = System::Hashing::storage_root();
+		let storage_root = new_header.state_root();
 		header.state_root().check_equal(&storage_root);
-		assert!(header.state_root() == &storage_root, "Storage root must match that calculated.");
+		assert!(header.state_root() == storage_root, "Storage root must match that calculated.");
 	}
 
 	/// Check a given transaction for validity. This doesn't execute any