message: package: fix env while using npm run release
diff: "build:firefox:prod": "cross-env NODE_ENV=prod gulp build --type production --browser firefox",
  "pack:chrome": "node tools/pack.js",
  "pack:firefox": "web-ext build -s dist -a artifacts",
  - "release": "npm run build:chrome:prod && npm run pack:chrome && npm run build:firefox:prod && npm run pack:firefox",
  + "release": "npm run build:chrome:prod && cross-env NODE_ENV=prod npm run pack:chrome && npm run build:firefox:prod && npm run pack:firefox",
  "release:firefox": "npm run build:firefox:prod && npm run pack:firefox && rimraf artifacts/dist-firefox.zip",
  "release:chrome": "npm run build:chrome:prod && cross-env NODE_ENV=prod npm run pack:chrome",
  "test": "gulp lint && npm run release",
  