Add nodemon config and watch command

nodemon.json

+{
+  "exec": "npm run dev",
+  "watch": ["src/*", "public/*"],
+  "ext": "js, html, css, json"
+}

package.json

@@ -9,7 +9,8 @@
     "dev": "NODE_ENV=development npm-run-all server",
     "clean": "rimraf dist",
     "build": "babel ./src --out-dir dist",
-    "prod": "NODE_ENV=production npm-run-all clean build server:prod"
+    "prod": "NODE_ENV=production npm-run-all clean build server:prod",
+    "watch": "nodemon"
   },
   "dependencies": {
     "cookie-parser": "~1.4.3",
@@ -23,6 +24,7 @@
     "@babel/cli": "^7.2.3",
     "@babel/core": "^7.2.2",
     "@babel/node": "^7.2.2",
-    "@babel/preset-env": "^7.3.1"
+    "@babel/preset-env": "^7.3.1",
+    "nodemon": "^1.18.9"
   }
 }