Enable rubocop-capybara which is included in rubocop-rspec gem

[eoinkelly]

We use Capybara all the time so this seems sensible. It also silences a warning from rubocop when you run it in the generated apps:

The following RuboCop extension libraries are installed but not loaded in config:
  * rubocop-capybara

You can opt out of this message by adding the following to your config (see https://docs.rubocop.org/rubocop/extensions.html#extension-suggestions for more options):
  AllCops:
    SuggestExtensions: false

[eoinkelly]

Bundler auto-generated this on my M1 Pro. Checking it in so that we don't see this diff again in future from other M1 users.