Select git branch to deploy with capistrano

config-deploy-staging.rb

server 'staging.domain.tld', :app, :web, :db, :primary => true

set :branch do
  default_tag = "master"
  tag = Capistrano::CLI.ui.ask "What tag/branch do you want to deploy? [#{default_tag}] "
  tag = default_tag if tag.empty?
  tag
end

set :rails_env,       'staging'
set :keep_releases,   2
set :port,            2222