no need to dup, argv is never mutated

railties/lib/rails/generators/rails/app/app_generator.rb

@@ -313,7 +313,7 @@ def get_builder_class
     # since it configures and mutates ARGV correctly.
     class ARGVScrubber # :nodoc
       def initialize(argv = ARGV)
-        @argv = argv.dup
+        @argv = argv
       end
 
       def prepare!