Capistrano 3 with Git Submodules

git.cap

# Save this file as lib/capistrano/tasks/git.cap

namespace :git do
  desc 'Copy repo to releases'
  task create_release: :'git:update' do
    on roles(:all) do
      with fetch(:git_environmental_variables) do
        within repo_path do
          execute :git, :clone, '-b', fetch(:branch), '--recursive', '.', release_path
        end
      end
    end
  end
end

I got NameError: uninitialized constant Capistrano::Git in Capistrano 3.6.0