added cross-env for npm run start command also

Author: suman mahto

package.json

@@ -8,7 +8,7 @@
     "url": "https://github.com/davellanedam/node-express-mongodb-jwt-rest-api-skeleton.git"
   },
   "scripts": {
-    "start": "NODE_ENV=production pm2 start server.js",
+    "start": "cross-env NODE_ENV=production pm2 start server.js",
     "mocha": "nyc mocha --timeout=5000 --exit",
     "test": "npm run fresh && npm run mocha",
     "dev": "cross-env NODE_ENV=development nodemon server.js",