title: Migrations: change column from integer to string
body: <p>Can anyone show me how to edit the following migration to change <code>:phone</code> integer to string?</p>
  
  <pre><code>class CreateContactInfos &lt; ActiveRecord::Migration
    def change
      create_table :contact_infos do |t|
        t.integer :phone
        t.string :facebook
        t.references :user
  
        t.timestamps 
      end
      add_index :contact_infos, :user_id
    end
  end
  </code></pre>
  
  <p>Thanks in advance!</p>