Decode code correctly (length-prefixed) (#168)

package.json

@@ -8,6 +8,10 @@
   "workspaces": [
     "packages/*"
   ],
+  "resolutions": {
+    "babel-core": "^7.0.0-bridge.0",
+    "typescript": "^2.9.2"
+  },
   "scripts": {
     "build": "polkadot-dev-build-ts",
     "check": "tslint --project . && tsc --noEmit",
@@ -16,7 +20,7 @@
     "test": "jest --coverage"
   },
   "devDependencies": {
-    "@polkadot/dev": "^0.20.9",
+    "@polkadot/dev": "^0.20.11",
     "@polkadot/ts": "^0.1.8"
   }
 }