Use child nameing in argument mutator

lib/mutant/mutator/node/argument.rb

@@ -7,6 +7,8 @@ module Mutant
         handle(:arg)
 
         UNDERSCORE = '_'.freeze
+
+        children :name
         NAME_INDEX = 0
 
       private
@@ -34,17 +36,6 @@ module Mutant
           end
         end
 
-        # Return name
-        #
-        # @return [Symbol]
-        #
-        # @api private
-        #
-        def name
-          children[NAME_INDEX]
-        end
-        protected :name
-
         # Test if argument mutation is skipped
         #
         # @return [true]