Can't run in headless mode

[evandev]

macOS Sierra 10.13.3

Using the default Desktop tag:
Cucumber::Rake::Task.new(:desktop, 'Runs test tagged as Desktop') do |t| t.cucumber_opts = "features/* --format html --out=results/desktop-report.html --format pretty --no-source --format rerun --out results/desktop-rerun.txt --tag @desktop" 'HEADLESS=true' end

And with env.rb set to the default:
if ENV['HEADLESS'] require 'headless' headless = Headless.new headless.start at_exit do headless.destroy end end

When I start my test
rake desktop /Users/USER/.rvm/rubies/ruby-2.5.0/bin/ruby -S bundle exec cucumber features/* --format html --out=results/desktop-report.html --format pretty --no-source --format rerun --out results/desktop-rerun.txt --tag @tms_desktop 'HEADLESS=true'

However, my test does not start in headless mode as expected. Any advice? As a side note I want to thank you for this excellent open source project, it's been a huge help!