Bump @polkadot/dev (#34)

package.json

@@ -10,7 +10,7 @@
     "test": "jest --coverage"
   },
   "devDependencies": {
-    "@polkadot/dev": "^0.12.6",
+    "@polkadot/dev": "^0.13.1",
     "lerna": "^2.5.1"
   }
 }

yarn.lock

@@ -54,9 +54,9 @@
     lodash "^4.2.0"
     to-fast-properties "^2.0.0"
 
-"@polkadot/dev@^0.12.6":
-  version "0.12.6"
-  resolved "https://registry.yarnpkg.com/@polkadot/dev/-/dev-0.12.6.tgz#1b2ffec13b3ebfc0a0e58253ee5eb8495482d91d"
+"@polkadot/dev@^0.13.1":
+  version "0.13.1"
+  resolved "https://registry.yarnpkg.com/@polkadot/dev/-/dev-0.13.1.tgz#7fd7bb6f5d343b0bbfa277abe24c46de909e854c"
   dependencies:
     babel-cli "^6.26.0"
     babel-core "^6.26.0"