[build] add cross-env on package.json

frontend/package.json

@@ -9,7 +9,9 @@
     "test:e2e": "vue-cli-service test:e2e",
     "lint": "vue-cli-service lint",
     "start": "npm run serve",
-    "build2": "npm run build"
+    "build2": "npm run build",
+    "crossbuild": "cross-env vue-cli-service build",
+    "crossbuild2": "cross-env npm run build"
   },
   "dependencies": {
     "apollo-boost": "^0.4.9",