{
  "name": "react-backend",
  "version": "0.0.0",
  "private": true,
  "scripts": {
    "start": "node ./bin/www",
    "heroku-postbuild": "cd client && yarn --production=false && yarn run build"
  },
  "dependencies": {
    "body-parser": "^1.17.2",
    "cookie-parser": "^1.4.3",
    "debug": "~2.6.3",
    "express": "~4.15.2",
    "jade": "^1.11.0",
    "mongoose": "^4.10.8",
    "morgan": "^1.8.2",
    "serve-favicon": "^2.4.3",
    "zombie": "^5.0.5"
  }
}

{
  "name": "react-backend",
  "version": "0.0.0",
  "private": true,
  "scripts": {
    "start": "node ./bin/www",
    "heroku-postbuild": "cd client && yarn --production=false && yarn run build"
  },
  "dependencies": {
    "body-parser": "^1.17.2",
    "cookie-parser": "^1.4.3",
    "debug": "~2.6.3",
    "express": "~4.15.2",
    "jade": "^1.11.0",
    "mongoose": "^4.10.8",
    "morgan": "^1.8.2",
    "serve-favicon": "^2.4.3",
    "zombie": "^5.0.5"
  },
  "devDependencies": {
    "yarn": "^0.24.5"
  }
}

Add yarn as dev dependency
Add yarn as dev dependency
