More Rubocop tweaks.

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

Library/.rubocop.yml

@@ -85,6 +85,8 @@ Style/GuardClause:
 # depends_on a: :b looks weird in formulae.
 Style/HashSyntax:
   EnforcedStyle: hash_rockets
+  Exclude:
+    - '**/cmd/**/*'
 
 # disabled until it respects line length
 Style/IfUnlessModifier:

Library/Homebrew/.rubocop.yml

@@ -20,7 +20,7 @@ Lint/NestedMethodDefinition:
 
 # so many of these in formulae but none in here
 Lint/ParenthesesAsGroupedExpression:
-  Enabled: false
+  Enabled: true
 
 Metrics/ModuleLength:
   CountComments: false