updating define_attribute_methods documentation

activemodel/README.rdoc

@@ -41,7 +41,7 @@ behavior out of the box:
       include ActiveModel::AttributeMethods
 
       attribute_method_prefix 'clear_'
-      define_attribute_methods [:name, :age]
+      define_attribute_methods :name, :age
 
       attr_accessor :name, :age
 

activemodel/lib/active_model/dirty.rb

@@ -30,7 +30,7 @@ module ActiveModel
   #
   #     include ActiveModel::Dirty
   #
-  #     define_attribute_methods [:name]
+  #     define_attribute_methods :name
   #
   #     def name
   #       @name

activemodel/test/cases/dirty_test.rb

@@ -3,7 +3,7 @@
 class DirtyTest < ActiveModel::TestCase
   class DirtyModel
     include ActiveModel::Dirty
-    define_attribute_methods [:name, :color]
+    define_attribute_methods :name, :color
 
     def initialize
       @name = nil

guides/source/active_model_basics.textile

@@ -20,7 +20,7 @@ class Person
 
   attribute_method_prefix 'reset_'
   attribute_method_suffix '_highest?'
-  define_attribute_methods ['age']
+  define_attribute_methods 'age'
 
   attr_accessor :age
 
@@ -99,7 +99,7 @@ require 'active_model'
 
 class Person
   include ActiveModel::Dirty
-  define_attribute_methods [:first_name, :last_name]
+  define_attribute_methods :first_name, :last_name
 
   def first_name
     @first_name