Added cross-env to support NODE_ENV in other OS

Author: gokulkrishh

package.json

@@ -12,6 +12,7 @@
     "babel-loader": "^6.2.8",
     "babel-preset-es2015": "^6.18.0",
     "copy-webpack-plugin": "^4.0.1",
+    "cross-env": "^5.0.1",
     "css-loader": "^0.26.1",
     "extract-text-webpack-plugin": "^2.1.0",
     "html-webpack-plugin": "^2.24.1",
@@ -28,6 +29,6 @@
   "scripts": {
     "start": "webpack-dev-server --hot --inline --open",
     "deploy": "npm run build && bash deploy.sh",
-    "build": "NODE_ENV=production webpack -p --config webpack.config.js"
+    "build": "cross-env NODE_ENV=production webpack -p --config webpack.config.js"
   }
 }