added prettier for js formatting. use 'npm run format'

package.json

@@ -3,6 +3,7 @@
   "version": "1.0.0",
   "description": "",
   "scripts": {
+    "format": "prettier --single-quote --write 'public/*.js' 'app.js'",
     "test": "echo \"Error: no test specified\" && exit 1",
     "start": "node app.js"
   },
@@ -14,6 +15,7 @@
     "express": "^4.15.3",
     "fs-extra": "^3.0.1",
     "path": "^0.12.7",
+    "prettier": "^1.3.1",
     "redis": "^2.7.1"
   }
 }