chore(npm): add espower-loader to DevDependencies

Author: azu

package.json

@@ -21,6 +21,7 @@
     "espower-loader": "^1.0.0"
   },
   "devDependencies": {
+    "espower-loader": "^1.0.0",
     "mocha": "^2.0.1"
   }
 }