まだプログラミングを勉強し始めて半年なのですが、
Heroku+Rails+Gruntのデプロイをしようと思っております。

先日こちらの記事（http://qiita.com/icb54615/items/e5d4db164c5002e4b183）を教えていただいたのですが、

    $ git push heroku master
Fetching repository, done.
Counting objects: 24, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (14/14), done.
Writing objects: 100% (24/24), 3.24 KiB | 0 bytes/s, done.
Total 24 (delta 14), reused 17 (delta 8)

-----> Fetching custom git buildpack... done
-----> Multipack app detected
=====> Downloading Buildpack: https://github.com/getgamba/heroku-buildpack-nodejs-grunt-compass.git

 !     Push rejected, failed to compile Multipack app

というエラーが出てしまいます。

アドバイスをいただけますと幸いです。

よろしくお願いいたします。

/root/.buildpacks

https://github.com/getgamba/heroku-buildpack-nodejs-grunt-compass.git
https://github.com/heroku/heroku-buildpack-ruby.git

/root/front/package.json

    {
  "name": "front",
  "version": "0.0.0",
  "dependencies": {},
  "devDependencies": {
    "grunt": "^0.4.5",
    "grunt-autoprefixer": "^0.7.3",
    "grunt-concurrent": "^0.5.0",
    "grunt-connect-proxy": "^0.1.11",
    "grunt-contrib-clean": "^0.5.0",
    "grunt-contrib-compass": "^0.7.2",
    "grunt-contrib-concat": "^0.4.0",
    "grunt-contrib-connect": "^0.7.1",
    "grunt-contrib-copy": "^0.5.0",
    "grunt-contrib-cssmin": "^0.9.0",
    "grunt-contrib-htmlmin": "^0.3.0",
    "grunt-contrib-imagemin": "^0.8.1",
    "grunt-contrib-jshint": "^0.10.0",
    "grunt-contrib-uglify": "^0.4.0",
    "grunt-contrib-watch": "^0.6.1",
    "grunt-filerev": "^0.2.1",
    "grunt-google-cdn": "^0.4.0",
    "grunt-karma": "^0.10.1",
    "grunt-newer": "^0.7.0",
    "grunt-ng-annotate": "^0.4.0",
    "grunt-ngmin": "^0.0.3",
    "grunt-protractor-runner": "^1.1.0",
    "grunt-rails-server": "^0.1.0",
    "grunt-shell-spawn": "^0.3.0",
    "grunt-svgmin": "^0.4.0",
    "grunt-usemin": "^2.1.1",
    "grunt-wiredep": "^1.7.0",
    "jasmine-core": "^2.1.3",
    "jshint-stylish": "^0.2.0",
    "karma": "^0.12.31",
    "karma-jasmine": "^0.3.4",
    "karma-phantomjs-launcher": "^0.1.4",
    "load-grunt-tasks": "^0.4.0",
    "source-map": "^0.1.37",
    "time-grunt": "^0.3.1"
  },
  "engines": {
    "node": ">=0.10.0"
  },
  "scripts": {
    "test": "grunt test"
  }
}