Actually this was where I made the improvement in performance in 3b7d7cb.

```ruby
disabled_lines_for_cops[cop_name] += [line_number]
```

This expression wastefully:

* creates a new array instance for `[line_number]`
* creates a new array instance for `disabled_lines_for_cops[cop_name] + [line_number]`
* removes the previous array instance in `disabled_lines_for_cops[cop_name]`