Composer install报错！
Composer 是 PHP 的一个依赖管理工具。它允许你申明项目所依赖的代码库，它会在你的项目中为你安装他们。Composer 不是一个包管理器。是的，它涉及 "packages" 和 "libraries"，但它在每个项目的基础上进行管理，在你项目的某个目录中（例如 vendor）进行安装。默认情况下它不会在全局安装任何东西。因此，这仅仅是一个依赖管理。
执行composer install遇到错误：Your requirements could not be resolved to an installable set of packages. 这是因为不匹配composer.json要求的版本。
完整错误如下：Loading composer repositories with package information<br>
Installing dependencies (including require-dev) from lock file<br>
Your requirements could not be resolved to an installable set of packages.<br>
<br>
Problem 1<br>
- Installation request for arcanedev/support 3.17.0 -> satisfiable by arcanedev/support[3.17.0].<br>
- arcanedev/support 3.17.0 requires php >=5.6 -> your PHP version (5.5.12) does not satisfy that requirement.<br>
Problem 2<br>
- Installation request for laravelista/ekko 1.2.3 -> satisfiable by laravelista/ekko[1.2.3].<br>
- laravelista/ekko 1.2.3 requires php >=5.6.0 -> your PHP version (5.5.12) does not satisfy that requirement.<br>
Problem 3<br>
- Installation request for league/flysystem 1.1.x-dev -> satisfiable by league/flysystem[1.1.x-dev].<br>
- league/flysystem 1.1.x-dev requires php >=5.6.0 -> your PHP version (5.5.12) does not satisfy that requirement.<br>
Problem 4<br>
- Installation request for league/flysystem dev-master -> satisfiable by league/flysystem[dev-master].<br>
- league/flysystem dev-master requires php >=5.6.0 -> your PHP version (5.5.12) does not satisfy that requirement.<br>
Problem 5<br>
- league/flysystem 1.1.x-dev requires php >=5.6.0 -> your PHP version (5.5.12) does not satisfy that requirement.<br>
- laravel/framework 5.2.x-dev requires league/flysystem ~1.0 -> satisfiable by league/flysystem[1.1.x-dev].<br>
- Installation request for laravel/framework 5.2.x-dev -> satisfiable by laravel/framework[5.2.x-dev].提示我的PHP 7版本太高，不符合composer.json需要的版本，但是在PHP 7下应该也是可以运行的，composer可以设置忽略版本匹配，命令是：composer install --ignore-platform-reqs<br>
or<br>
composer update --ignore-platform-reqs再次执行composer命令可以正常安装包了。
设置composer为国内镜像【速度】composer config -g repo.packagist composer https://packagist.phpcomposer.com
