DM migration issue

gistfile1.rb

require 'dm-core'
require 'dm-migrations'
require 'dm-migrations/migration_runner'

DataMapper.setup(:default,{
  :adapter=>'mysql',
  :database=>'datamapper_test',
  :username=>'root',
  :password=>'',
  :host=>'127.0.0.1'
})

DataMapper::Logger.new(STDOUT, :debug)
DataMapper.logger.debug( "Starting Migration" )

class Person
  include DataMapper::Resource

  property :id, Serial
  property :name, Text
  property :age, Integer
end

task :default

task :migrate_down do
  migrate_down!
end

task :migrate_up do
  migrate_up!
end

migration 1, :create_person_table do
  up do
    create_table :people do
      column :id,   Integer, :serial => true
      column :name, String, :length=>2
      column :age,  Integer
    end
    modify_table :people do
      change_column :name, String, :length=>2
    end
  end

  down do
    drop_table :people
  end
end