Undefined method 'patch' - routing error

I am starting to develop Rails and MVC and need help below:

I am doing an example at http://edgeguides.rubyonrails.org/getting_started.html

In "5.12 Updating Messages" we are asked to add the following to our config / routes.rb:

patch "posts/:id" => "posts#update"

      

        
        
        
      

    

If I do this and run rake routes

, I get the following error:

undefined method `patch' for #<ActionDispatch::Routing::Mapper:0x390f078>

      

        
        
        
      

    

I am getting the same error when I go - http://localhost:3000/posts/1

This is the line in the edit.html.erb file:

<%= form_for :post, url: { action: :update, id: @post.id }, method: :patch do |f| %>

      

        
        
        
      

    

I have Rails 3.2.1.

Environment:

I am doing this on Windows 7. I installed Rails via railsinstaller.org. Browsers - Chrome, Firefox