improve example in migrations docs, closes #6370

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@5275 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/lib/active_record/migration.rb

@@ -157,7 +157,7 @@ def initialize(version)
   #       add_column :people, :salary, :integer
   #       Person.reset_column_information
   #       Person.find(:all).each do |p|
-  #         p.salary = SalaryCalculator.compute(p)
+  #         p.update_attribute :salary, SalaryCalculator.compute(p)
   #       end
   #     end
   #   end
@@ -177,7 +177,7 @@ def initialize(version)
   #     ...
   #     say_with_time "Updating salaries..." do
   #       Person.find(:all).each do |p|
-  #         p.salary = SalaryCalculator.compute(p)
+  #         p.update_attribute :salary, SalaryCalculator.compute(p)
   #       end
   #     end
   #     ...