Revert "Updated migration generator template."

Rails 3.0.x doesn't support new migration style

This reverts commit b7bfdec3.

generators/paperclip/templates/paperclip_migration.rb.erb

 class <%= migration_name %> < ActiveRecord::Migration
-  def change
+  def self.up
 <% attachments.each do |attachment| -%>
     add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_file_name, :string
     add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_content_type, :string
     add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_file_size, :integer
     add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_updated_at, :datetime
-    add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_fingerprint, :string, length: 32
+<% end -%>
+  end
+
+  def self.down
+<% attachments.each do |attachment| -%>
+    remove_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_file_name
+    remove_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_content_type
+    remove_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_file_size
+    remove_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_updated_at
 <% end -%>
   end
 end