I execute
$ heroku run rake assets:clean Running `rake assets:clean` attached to terminal... up, run.2 /usr/local/bin/ruby /app/vendor/bundle/ruby/1.9.1/bin/rak
The rake assets:clean functionality has been replaced with
rake assets:clobber
in the latest version of Rails.
https://github.com/rails/sprockets-rails/blob/master/README.md