iCheck/all couldn't find

Hello,
when i  add iCheck to application.css give me a error.

My application.css:

``` css
 *= require_self
 *= require bootstrap
 *= require font-awesome
 *= require ionicons
 *= require admin-lte
 *= require iCheck/all
 *= require datatables/dataTables.bootstrap
 *= require_tree .
```

Error:

```
couldn't find file 'iCheck/all' with type 'text/css'`
```
