Enable Style/MethodDefParentheses rule

Enable parenthesis for method definitions so that
we have more consistency in the codebase. In
addition to that, I disabled running RuboCop on
generated parser files.

Author: vinistock

.rubocop.yml

@@ -2,6 +2,14 @@ AllCops:
   TargetRubyVersion: 3.0
   DisabledByDefault: true
   SuggestExtensions: false
+  Exclude:
+    # Exclude files that are auto generated
+    - "lib/rdoc/rd/block_parser.rb"
+    - "lib/rdoc/rd/inline_parser.rb"
+    - "lib/rdoc/markdown.rb"
+    - "lib/rdoc/markdown/literals.rb"
+    # Exclude dependency files when installing them under vendor
+    - "vendor/**/*"
 
 Layout/TrailingWhitespace:
   Enabled: true
@@ -20,3 +28,6 @@ Layout/SpaceAfterComma:
 
 Lint/UnreachableCode:
   Enabled: true
+
+Style/MethodDefParentheses:
+  Enabled: true