Let StorageDoubleMap use borrowed key types (#1804)

* Let StorageDoubleMap use borrowed key types

* Bump impl version

substrate/node/runtime/src/lib.rs

@@ -61,7 +61,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	impl_name: create_runtime_str!("substrate-node"),
 	authoring_version: 10,
 	spec_version: 30,
-	impl_version: 32,
+	impl_version: 30,
 	apis: RUNTIME_API_VERSIONS,
 };