title: ruby on rails rake db:migrate error
body: <p>i'm starting to learn ruby on rails using this guide : 
  <a href="http://guides.rubyonrails.org/getting_started.html" rel="noreferrer">getting_started</a>  , i created my project and database but when i run rake db:migrate i get this error:</p>
  
  <blockquote>
    <p>@mona-Extensa-5230:~/rubyDev/Sites/blog# rake db:migrate<br>
    (in /home/mona/rubyDev/Sites/blog)<br>
    ==  CreatePosts: migrating ====================================================
    -- create_table(:posts)<br>
    rake aborted!<br>
    An error has occurred, this and all later migrations canceled:<br>
    private method `String' called for#<br>
    ActiveRecord::ConnectionAdapters::TableDefinition:0xb7540f30></p>
  </blockquote>
  
  <p>thanks.</p>