Fix rubocop issues preventing successful builds in master.

All builds are failing with:

```
Offences:
app/controllers/filters_controller.rb:82:15: C: has_key? is deprecated in favor of key?.
    if params.has_key?(:products)
              ^^^^^^^^
754 files inspected, 1 offence detected
```

See https://travis-ci.org/Katello/katello/jobs/11529563 for example.