Fix incorrect query

rails4_acts_as_paranoid.rb
```rails4_acts_as_paranoid.rb
138: class_attribute :paranoid_configuration, :paranoid_column_reference
```

class_attribute doesn't duplicate instance.
http://apidock.com/rails/Class/class_attribute


```rails4_acts_as_paranoid.rb
213: columns = secondary_paranoid_columns.push(primary_paranoid_column)
```

Appending in child changes both parent and child because paranoid_configuration is the same object.

 
 
secondary_paranoid_columns variable and SQL statement would be as follow when has destroyed model several times.


secondary_paranoid_columns
```
[
  {:column=>"deleted_at", :column_type=>"time", :recover_dependent_associations=>true, :dependent_recovery_window=>120 seconds},
  {:column=>"deleted_at", :column_type=>"time", :recover_dependent_associations=>true, :dependent_recovery_window=>120 seconds}, 
  {:column=>"deleted_at", :column_type=>"time", :recover_dependent_associations=>true, :dependent_recovery_window=>120 seconds}
  
  .....
 
]
```


SQL statement

```
UPDATE `hoge` SET deleted_at = '2013-10-15 00:00:00', deleted_at = '2013-10-15 00:00:00', deleted_at = '2013-10-15 00:00:00', .....
```


with this bug fixes.