use nodemon to watch for changes to webpack config and restart the dev server when necessary

Former-commit-id: cb2c762d

package.json

 {
   "private": true,
   "scripts": {
-    "dev-server": "webpack-dev-server --config config/webpack.config.js",
+    "dev-server": "nodemon --watch config/webpack.config.js -- ./node_modules/.bin/webpack-dev-server --config config/webpack.config.js",
     "eslint": "eslint --max-warnings 0 --ext .js,.vue .",
     "eslint-fix": "eslint --max-warnings 0 --ext .js,.vue --fix .",
     "eslint-report": "eslint --max-warnings 0 --ext .js,.vue --format html --output-file ./eslint-report.html .",
@@ -70,6 +70,7 @@
     "karma-phantomjs-launcher": "^1.0.2",
     "karma-sourcemap-loader": "^0.3.7",
     "karma-webpack": "^2.0.2",
+    "nodemon": "^1.11.0",
     "webpack-dev-server": "^2.4.2"
   }
 }