rake assets:precompile
rake aborted!
rails_admin/timeline/arrow_left.png isn't precompiled
  (in /home/brunto/.bundler/ruby/1.9.1/rails_admin-93966e148c0f/app/assets/stylesheets/rails_admin/ra.timeline.css.erb)

Tasks: TOP => assets:precompile
(See full trace by running task with --trace)