:sparkles: mod pipline to npm build | added build option to package.json

.drone.yml

   commands:
   - cd ./vue-theme
   - npm install
-  - npm test
+  - npm test
+
+- name: build
+  image: node
+  commands:
+  - cd ./vue-theme
+  - npm install
+  - npm build

vue-theme/package.json

   "main": "index.js",
   "scripts": {
     "dev": "webpack-dev-server --hot",
+    "build": "webpack -p --env.production --progress --hide-modules",
     "test": "echo running contrived example command..."
   },
   "keywords": [