Add this line to your application's Gemfile:
gem 'capistrano-scm-gitsubmodules'
And then execute:
$ bundle
Or install it yourself as:
$ gem install capistrano-scm-gitsubmodules
Add require 'capistrano/gitsubmodules' to your Capfile
set scm: 'gitsubmodules'
This wil make capistrano require the tasks.
This gem replaces the archive technique with a clone. So release folders will be clones of the repo folder, instead of just plain files, similar to capistrano 2.