Remove default hasher (#4739)

* remove default hasher from decl_storage!

* fix decl_storage declarations

substrate/frame/assets/src/lib.rs

@@ -228,11 +228,11 @@ decl_error! {
 decl_storage! {
 	trait Store for Module<T: Trait> as Assets {
 		/// The number of units of assets held by any given account.
-		Balances: map (T::AssetId, T::AccountId) => T::Balance;
+		Balances: map hasher(blake2_256) (T::AssetId, T::AccountId) => T::Balance;
 		/// The next asset identifier up for grabs.
 		NextAssetId get(fn next_asset_id): T::AssetId;
 		/// The total unit supply of an asset.
-		TotalSupply: map T::AssetId => T::Balance;
+		TotalSupply: map hasher(blake2_256) T::AssetId => T::Balance;
 	}
 }