fix: `profile_image_url` isnt used in settings

![screen shot 2014-02-27 at 12 07 14](https://f.cloud.github.com/assets/1935767/2271955/15bb4128-9f00-11e3-95d7-2ec000a2c03b.png)

我查看`POST /settings`的request的form data如下：
```
name:yorkie
email:yorkiefixer@gmail.com
url:http://yorkiefixer.me
location:Beijing, China
signature:
profile:https://github.com/yorkie
weibo:
github:yorkie
receive_at_mail:on
receive_reply_mail:on
action:change_setting
```

/cc @alsotang :)