Configure solidus_chrome_headless as capybara-screenshot driver

We have a custom driver. Capybara-screenshot needs to know
about it.

Author: tvdeyen

lib/solidus_dev_support/rspec/feature_helper.rb

@@ -12,6 +12,10 @@
 require 'capybara-screenshot/rspec'
 require 'solidus_dev_support/rspec/capybara'
 
+Capybara::Screenshot.register_driver(:solidus_chrome_headless) do |driver, path|
+  driver.browser.save_screenshot(path)
+end
+
 def dev_support_assets_preload
   if Rails.application.respond_to?(:precompiled_assets)
     Rails.application.precompiled_assets