安装Forms & HTML

http://laravelcollective.com/docs/5.0/html
我参考这里安装但是composer update
出现以下错误
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

Problem 1
- laravel/framework v5.0.9 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.8 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.7 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.6 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.5 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.4 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.3 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.23 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.22 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.21 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.20 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.2 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.19 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.18 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.17 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.16 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.15 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.14 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.13 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.12 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.11 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.10 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.1 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.0 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- laravel/framework v5.0.16 requires ext-mcrypt * -> the requested PHP extension mcrypt is missing from your system.
- Installation request for laravel/framework 5.0.* -> satisfiable by laravel/framework[v5.0.0, v5.0.1, v5.0.10, v5.0.11, v5.0.12, v5.0.13, v5.0.14, v5.0.15, v5.0.16, v5.0.17, v5.0.18, v5.0.19, v5.0.2, v5.0.20, v5.0.21, v5.0.22, v5.0.23, v5.0.3, v5.0.4, v5.0.5, v5.0.6, v5.0.7, v5.0.8, v5.0.9].