Fixed missing ] in example

The last line was missing a `]` that I adjusted (and lined up the spacing for the remaining lines accordingly).

Changed 
```ruby
"status[#{user.active_campaign_list_id}" => user.receive_emails ? 1 : 2
```

to

```ruby
"status[#{user.active_campaign_list_id}]" => user.receive_emails ? 1 : 2
```