make gulp start on installation

Author: aprilla

package-lock.json

@@ -9,6 +9,7 @@
     "test": "nyc --check-coverage --lines 100 --functions 100 --branches 100 mocha app/tests",
     "coverage": "nyc report --reporter=text-lcov | node ./node_modules/coveralls/bin/coveralls.js",
     "lint": "./node_modules/.bin/eslint .",
+    "watch-dev": "gulp start-watcher",
     "serve": "node ./node_modules/http-server/bin/http-server"
   },
   "husky": {