This requires updating to Rubocop 0.49.0 which will require some fixes
to rules, in Homebrew/brew and Homebrew/homebrew-core but opening this
for now so I remember.

- Don't enforce hash rockets on external commands.
- Enabled accidentally disabled ParenthesesAsGroupedExpression.

Another look at the current Rubocop rules and how they fit with our
existing and desired future style. Almost all of these changes were
automatic. Split some rules between formulae/brew where brew doesn't
have millions of cases that need fixed.

This allows having a shared style that’s use for Homebrew/brew and taps
which can be overridden by Homebrew/brew.