use login better than name on plain format

```
# Ordered by date of first contribution.
# Auto-generated by 'contributors' on Sun, 19 Jan 2014 12:53:33 GMT.
# https://github.com/xingrz/node-contributors

fengmk2 <fengmk2@gmail.com> (https://github.com/fengmk2)
kof <oleg008@gmail.com> (https://github.com/kof)
```

it's better than 

```
# Ordered by date of first contribution.
# Auto-generated by 'contributors' on Sun, 19 Jan 2014 12:38:57 GMT.
# https://github.com/xingrz/node-contributors

fengmk2 <fengmk2@gmail.com> (https://github.com/fengmk2)
Oleg Slobodskoi <oleg008@gmail.com> (https://github.com/kof)
```

Because AUTHORS will auto add to package.json `contributors` property:

![image](https://f.cloud.github.com/assets/156269/1949468/e6b8b2c6-8108-11e3-99b6-3db52cb11c25.png) 

http://cnpmjs.org/package/charset