ruby-on-rails – 如何构建任务’部署：迁移’

cap aborted!
Don't know how to build task 'deploy:migrations'
/Users/marya/.rvm/gems/ruby-1.9.3-p448/gems/capistrano-3.2.1/lib/capistrano/application.rb:15:in `run'
/Users/marya/.rvm/gems/ruby-1.9.3-p448/gems/capistrano-3.2.1/bin/cap:3:in `<top (required)>'
/Users/marya/.rvm/gems/ruby-1.9.3-p448/bin/cap:23:in `load'
/Users/marya/.rvm/gems/ruby-1.9.3-p448/bin/cap:23:in `<main>'
(See full trace by running task with --trace)

的Gemfile：

# Use Capistrano to deploy on production server
group :development do
  gem 'capistrano','~> 3.2.0'
  gem 'capistrano-rails'
  gem 'capistrano-bundler'
  gem 'capistrano-rvm'
end

deploy.rb：

# config valid only for Capistrano 3.1
lock '3.2.1'

set :application,'someapp'

set :scm,:git
set :repo_url,'somerepo'

# Default branch is :master
# ask :branch,proc { `git rev-parse --abbrev-ref HEAD`.chomp }.call

# Default deploy_to directory is /var/www/my_app
# set :deploy_to,'/var/www/my_app'

# Default value for :scm is :git
# set :scm,:git

# Default value for :format is :pretty
# set :format,:pretty

# Default value for :log_level is :debug
# set :log_level,:debug

# Default value for :pty is false
# set :pty,true

# Default value for :linked_files is []
# set :linked_files,%w{config/database.yml}

# Default value for linked_dirs is []
# set :linked_dirs,%w{bin log tmp/pids tmp/cache tmp/sockets vendor/bundle public/system}

# Default value for default_env is {}
# set :default_env,{ path: "/opt/ruby/bin:$PATH" }

# Default value for keep_releases is 5
# set :keep_releases,5

namespace :deploy do

  desc 'Restart application'
  task :restart do
    on roles(:app),in: :sequence,wait: 5 do
      # Your restart mechanism here,for example:
      execute :touch,release_path.join('tmp/restart.txt')
    end
  end

  after :publishing,:restart
end

capfile.rb：

# Load DSL and Setup Up Stages
require 'capistrano/setup'

# Includes default deployment tasks
require 'capistrano/deploy'

# Includes tasks from other gems included in your Gemfile
#
# For documentation on these,see for example:
#
#   https://github.com/capistrano/rvm
#   https://github.com/capistrano/rbenv
#   https://github.com/capistrano/chruby
#   https://github.com/capistrano/bundler
#   https://github.com/capistrano/rails
#
require 'capistrano/rvm'
# require 'capistrano/rbenv'
# require 'capistrano/chruby'
require 'capistrano/bundler'
require 'capistrano/rails/assets'
require 'capistrano/rails/migrations'

# Loads custom tasks from `lib/capistrano/tasks' if you have any defined.
Dir.glob('lib/capistrano/tasks/*.rake').each { |r| import r }

如果我执行’cap production deploy’,那么一切都很好.我该如何解决？