Composer未更新所需的库

我正在使用Laravel框架，并希望包含GitHub中的库。这是我完整的composer.json文件：

{
    "name": "laravel/laravel",
    "description": "The Laravel Framework.",
    "keywords": ["framework", "laravel"],
    "license": "MIT",
    "require": {
        "laravel/framework": "4.0.*",
        "intervention/helper": "dev-master" <- this is what I've added
    },
    "autoload": {
        "classmap": [
            "app/commands",
            "app/controllers",
            "app/models",
            "app/validators",
            "app/database/migrations",
            "app/database/seeds",
            "app/tests/TestCase.php"
        ]
    },
    "scripts": {
        "post-install-cmd": [
            "php artisan optimize"
        ],
        "post-update-cmd": [
            "php artisan clear-compiled",
            "php artisan optimize"
        ],
        "post-create-project-cmd": [
            "php artisan key:generate"
        ]
    },
    "config": {
        "preferred-install": "dist"
    },
    "minimum-stability": "dev"
}

我在require指令下添加了"intervention/helper": "dev-master"，当我在网站的本地副本上执行composer update时，一切都很好，我可以使用库。

我做了一个git push和pull，把它放到我的实时服务器上，当做composer update时，它不会下载这个库。这是命令的全部输出：http://pastebin.com/UgPNTaDw

我还试了第二次composer install和composer update，但都不起作用。我还验证了git在实时服务器上检索到了新的composer.json文件，并且已经检索到了。

为什么composer没有意识到更改并下载库？