rubocop: don't always display cop names.

Library/.rubocop.yml

@@ -3,6 +3,7 @@ AllCops:
   Exclude:
     - '**/Casks/**/*'
     - '**/vendor/**/*'
+  DisplayCopNames: false
 
 require: ./Homebrew/rubocops.rb
 

Library/Homebrew/test/cmd/style_spec.rb

@@ -28,7 +28,7 @@ describe "brew style" do
       rubocop_result = Homebrew.check_style_json([formula])
 
       expect(rubocop_result.file_offenses(formula.realpath.to_s).map(&:message))
-        .to include("Layout/EmptyLinesAroundClassBody: Extra empty line detected at class body beginning.")
+        .to include("Extra empty line detected at class body beginning.")
     end
   end
 end