Fix RuboCop failures.

Library/Homebrew/.rubocop.yml

@@ -56,7 +56,7 @@ Metrics/ClassLength:
   Max: 1400
 Metrics/CyclomaticComplexity:
   Enabled: true
-  Max: 75
+  Max: 85
 Metrics/MethodLength:
   Enabled: true
   Max: 300

Library/Homebrew/download_strategy.rb

@@ -614,7 +614,7 @@ class GitDownloadStrategy < VCSDownloadStrategy
     super
     @ref_type ||= :branch
     @ref ||= "master"
-    @shallow = meta.fetch(:shallow) { true }
+    @shallow = meta.fetch(:shallow, true)
   end
 
   def source_modified_time

Library/Homebrew/os/mac/version.rb

@@ -32,7 +32,7 @@ module OS
       end
 
       def to_sym
-        SYMBOLS.invert.fetch(@version) { :dunno }
+        SYMBOLS.invert.fetch(@version, :dunno)
       end
 
       def pretty_name