Can only install one of: topthink/think-installer[v2.0.0, v1.0.12].

• 这种情况发生在:
  我要在自己的 ThinkPHP5.1.2框架中，使用 composer 命令安装 workerMan 拓展的时候所提示的信息

• composer 命令：composer require topthink/think-worker=v2.0.9

• 提示信息
  

• 打印信息如下：

./composer.json has been updated
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
    - Can only install one of: topthink/think-installer[v2.0.0, v1.0.12].
    - Can only install one of: topthink/think-installer[v2.0.0, v1.0.12].
    - Can only install one of: topthink/think-installer[v2.0.0, v1.0.12].
    - topthink/think-worker v2.0.9 requires topthink/think-installer ^2.0 -> satisfiable by topthink/think-installer[v2.0.0].
    - Installation request for topthink/think-worker v2.0.9 -> satisfiable by topthink/think-worker[v2.0.9].
    - Installation request for topthink/think-installer (locked at v1.0.12) -> satisfiable by topthink/think-installer[v1.0.12].


Installation failed, reverting ./composer.json to its original content.

• 通过对提示信息的阅读理解，说明当前的框架只让安装 v2.0.0, v1.0.12 的其中一个;
  也就是说，当前的 ThinkPHP 框架太低，不足以满足 v2.0.9 版本的 workerMan;
  解决方案就是： 安装一个较低版本的 workerMan呗！