Add deprecation warning for npm run dev

Author: acco

package.json

@@ -20,7 +20,8 @@
   "scripts": {
     "start": "concurrently \"npm run server\" \"npm run client\"",
     "server": "babel-node server.js",
-    "client": "babel-node start-client.js"
+    "client": "babel-node start-client.js",
+    "dev": "echo \"This command has been deprecated. Use 'npm start'\" && exit 1"
   },
   "devDependencies": {
     "concurrently": "^3.1.0"