Merge pull request #591 from pvdb/simplify_rake_system_dir

refactor: simplify `Rake::Application#system_dir` method

Author: hsbt

lib/rake/application.rb

@@ -755,14 +755,7 @@ def glob(path, &block) # :nodoc:
 
     # The directory path containing the system wide rakefiles.
     def system_dir # :nodoc:
-      @system_dir ||=
-        begin
-          if ENV["RAKE_SYSTEM"]
-            ENV["RAKE_SYSTEM"]
-          else
-            standard_system_dir
-          end
-        end
+      @system_dir ||= ENV["RAKE_SYSTEM"] || standard_system_dir
     end
 
     # The standard directory containing system wide rake files.