Added dependency badge for README file;

I would like to add VersionEye dependency badge, which shows a current state of dependencies and when user clicks on badge, then he/she will see an additional metadata, that doesnt exists on npmjs page, for example previous versions, release cycle and  sub-dependencies.
Yes, there is.  

```
![ Dependency Status ](https://www.versioneye.com/nodejs/request/badge.svg)](https://www.versioneye.com/nodejs/request)
```