当我使用laravel（在mac OSX Yosemite上）为我的家园composer install设置虚拟机时，我收到以下错误：
$ composer install
Warning: This development build of composer is over 30 days old. It is
recommended to update it by running "/usr/local/bin/composer self-update" to get the
latest version.
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Nothing to install or update
Generating autoload files
Mcrypt PHP extension required.
Script php artisan clear-compiled handling the post-install-cmd event returned
with an error
[RuntimeException]
Error Output:
install [--prefer-source] [--prefer-dist] [--dry-run]
[--dev] [--no-dev] [--no-plugins] [--no-custom-installers] [--no-autoloader]
[--no-scripts] [--no-progress] [-v|vv|vvv|--verbose] [-o|--optimize-autoloader]
[--ignore-platform-reqs] [packages1] ... [packagesN]
然后我运行命令$ brew install php5-mcrypt。我得到以下内容：
$ brew install php5-mcrypt
Error: No available formula for php5-mcrypt
Searching formulae...
Searching taps...
$
如何修复此问题并安装php5-mcrypt？