Disable Rubocop's `casecmp` preference
Disable Rubocop's `casecmp` preference

Rubocop wants us to use

```
c[k].to_s.casecmp(v.to_s).zero?
```

instead of

```
c[k].to_s.downcase == v.to_s.downcase
```

That's largely a micro-optimisation, and I'd prefer to stick with the
more legible version instead. So disable this check, (as we have also
done in other repos).

everypolitician/everypolitician-ruby,everypolitician/everypolitician-ruby