twitterコールバックでscreen_nameを保存する

$ rails g migration AddScreenNameToUser screen_name:string
/Users/yuta/tmp/rails/Twitter/config/initializers/devise.rb:255: warning: already initialized constant OpenSSL::SSL::VERIFY_PEER
      invoke  active_record
      create    db/migrate/20131022012752_add_screen_name_to_user.rb
$○ rake db:migrate
==  AddScreenNameToUser: migrating ============================================
-- add_column(:users, :screen_name, :string)
   -> 0.0033s
==  AddScreenNameToUser: migrated (0.0033s) ===================================