Grunt heroku deployment problem: package.json file

gistfile1.txt

{
  "name": "vincentiatreehouse",
  "description": "One pager site using grunt & foundation 5",
  "version": "0.0.1",
  "engines": {
    "node": "0.10.x",
    "npm": "1.3.x"
  },
  "devDependencies": {
    "grunt": "~0.4.1",
    "grunt-contrib-uglify": "~0.2.2",
    "grunt-contrib-concat": "~0.3.0",
    "grunt-contrib-sass": "~0.5.0",
    "grunt-contrib-imagemin": "~0.4.0",
    "grunt-contrib-watch": "~0.5.3",
    "grunt-contrib-connect": "~0.5.0",
    "grunt-autoprefixer": "~0.4.1",
    "grunt-contrib-cssmin": "~0.7.0",
    "grunt-contrib-jshint": "~0.7.2",
    "grunt-contrib-haml": "~0.1.1",
    "grunt-contrib-coffee": "~0.7.0"
  },
  "dependencies": {
    "load-grunt-tasks": "~0.2.0"
  }
}