无法检测到Node.js Heroku部署语言

Question

Counting objects: 64, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (58/58), done.
Writing objects: 100% (64/64), 541.82 KiB | 12.90 MiB/s, done.
Total 64 (delta 15), reused 0 (delta 0)
remote: Compressing source files... done.
remote: Building source:
remote:
remote:  !     No default language could be detected for this app.
remote:                         HINT: This occurs when Heroku cannot detect the buildpack to use for this application automatically.
remote:                         See https://devcenter.heroku.com/articles/buildpacks
remote:
remote:  !     Push failed
remote: Verifying deploy...
remote:
remote: !       Push rejected to stockandtrack.
remote:

尝试将Node.js应用程序推送到Heroku时出现上述错误。我已验证我的package.json在根文件夹中，并且已将引擎声明添加到我的package.json中。我继续收到此错误。以下是我的package.json和文件夹结构：

    {
  "name": "test",
  "version": "1.0.0",
  "engines": {
    "node": "8.9.4"
  },
  "main": "server.js",
  "scripts": {
    "start": "if-env NODE_ENV=production && yarn run start:prod || yarn run start:dev",
    "start:prod": "node server.js",
    "start:dev": "concurrently \"nodemon --ignore 'client/*'\" \"yarn run client\"",
    "client": "cd client && yarn run start",
    "install": "cd client && yarn install",
    "build": "cd client && yarn run build",
    "heroku-postbuild": "yarn run build"
  },
  "dependencies": {
    "cors": "^2.8.4",
    "express": "^4.16.3",
    "mysql": "^2.16.0",
    "path": "^0.12.7"
  },
  "devDependencies": {
    "concurrently": "^3.5.0",
    "nodemon": "^1.11.0"
  }
}

任何帮助将不胜感激！