action_item deprecation warning.

I am using active_admin(1.0.0.pre2) with active_admin_csv_import(1.3.1) in a rails 4.1 application. When using the DSL as

``` ruby
csv_importable :columns => [:name, :email, :password]
```

the warning displayed upon starting the server are:

 WARN -- : DEPRECATION WARNING: Active Admin: using `action_item` without a name is deprecated! Use `action_item(:edit)`.
