[frontend] fix frontend build error (#229)

Author: Msquittto

app-engine/frontend/package.json

@@ -7,8 +7,8 @@
     "start": "webpack serve --progress --profile --mode development --host localhost --port 3310 --config webpack.dev.js",
     "start:single": "webpack serve --config webpack.dev.single.js",
     "start:plugin": "bash ./plugins/plugin.sh && npm run start",
-    "build:prod": "npm run build:plugin:prod && webpack --mode production --config webpack.prod.js",
-    "build:single": "npm run build:plugin:single  && webpack --mode production  --config webpack.prod.single.js",
+    "build:prod": "webpack --mode production --config webpack.prod.js",
+    "build:single": "webpack --mode production  --config webpack.prod.single.js",
     "build:plugin:prod": "bash ./plugins/plugin.sh prod",
     "build:plugin:single": "bash ./plugins/plugin.sh prod spa"
   },