tj/co — pull request #161 by fengmk2 (2014-11-16 07:44:09+00:00)
Title: add 'engines' property on package.json

Let npm show warnning info when user current node version not match:

```bash
npm WARN engine co@4.0.0: wanted: {"node":">= 0.11.13"} (current: {"node":"0.10.33","npm":"1.4.0"})
```