A Heroku update

I've added a note to Section 2.3.5 (Deploying the demo app) about pushing data as well as data models up to Heroku. This uses the taps gem (along with the main heroku gem), which has recently been updated by Heroku. Ruby on Rails Tutorial readers using Heroku should update both gems per this Heroku blog post on supporting large data sets:

$ [sudo] gem update heroku taps

(As indicated by the square brackets, many users will need to use sudo to install gems, but users of Ruby Version Manager (rvm) should omit it.)