Rails - Apr 2006 - Migrate default now()

I want to set default value to current time of database:

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      # ...
      t.column :created_at, :timestamp, :null => false, :default =>
''now''
    end
  end
  #...
end

On postgresql, it is converted to:
created_at timestamp NOT NULL DEFAULT ''2006-04-25
11:34:45.725837''::timestamp without time zone

Modify to:
t.column :created_at, :timestamp, :null => false, :default =>
''current_timestamp''

It is converted to:
created_at timestamp NOT NULL DEFAULT ''current_timestamp''
It''s wrong.

I try to fixed it:
default_fix.rb:
module ActiveRecord
  module ConnectionAdapters # :nodoc:
    module SchemaStatements
      def add_column_options!(sql, options) #:nodoc:
        unless options[:default].nil?
          if options[:default] == "now"
            sql << " DEFAULT #{now(options[:default],
options[:column])}"
          else
            sql << " DEFAULT #{quote(options[:default],
options[:column])}" unless options[:default].nil?
          end
        end
        sql << " NOT NULL" if options[:null] == false
      end
    end
  end
end

module ActiveRecord
  module ConnectionAdapters
    class PostgreSQLAdapter < AbstractAdapter
      def now(value, column)
        "current_timestamp"
      end
    end
  end
end

test code:
class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      # ...
      t.column :created_at, :timestamp, :null => false, :default =>
''now''
    end
  end
  #...
end


It works find. but is this way correct?