安装Bootstrap后，Assetic转储产生解析错误

Question

我刚刚在Symfony 2项目中安装了leafo/lessphp和twitter/bootstrap，但在进行资产转储时遇到了问题。

我已经添加了以下两个软件包，并完成了composer update。

"require": {
        "php": ">=5.3.3",
        "symfony/symfony": "~2.4",
        "doctrine/orm": "~2.2,>=2.2.3",
        "doctrine/doctrine-bundle": "~1.2",
        "twig/extensions": "~1.0",
        "symfony/assetic-bundle": "~2.3",
        "symfony/swiftmailer-bundle": "~2.3",
        "symfony/monolog-bundle": "~2.4",
        "sensio/distribution-bundle": "~2.3",
        "sensio/framework-extra-bundle": "~3.0",
        "sensio/generator-bundle": "~2.3",
        "incenteev/composer-parameter-handler": "~2.0",
        "leafo/lessphp": "~0.4.0",
        "twitter/bootstrap": "*",
        "components/jquery": "dev-master"
    }

然后，Assetic转储（php app/console assetic:dump --force）会产生此错误：

Dumping all dev assets. Debug mode is on.

[Exception]   parse error: failed at `&:extend(.clearfix all);` /var/www/vhosts/dev/dev_ayrshireminis/app/../vendor/twitter/bootstrap/less/mixins.l ess on line 643     

assetic:dump [--watch] [--force] [--period="..."] [write_to]

我是否需要更新？为什么会发生这种错误？