Make protected branches spec work in headless Chrome

This needs two patches in Capybara:

* https://github.com/teamcapybara/capybara/pull/1902
* https://github.com/teamcapybara/capybara/pull/1903

spec/features/projects/branches_spec.rb

@@ -93,7 +93,11 @@ describe 'Branches' do
 
         expect(page).to have_content('fix')
         expect(find('.all-branches')).to have_selector('li', count: 1)
-        find('.js-branch-fix .btn-remove').click
+        # To work with Chrome headless, this needs an updated version of
+        # Capybara with two bug fixes:
+        # * https://github.com/teamcapybara/capybara/pull/1902/
+        # * https://github.com/teamcapybara/capybara/pull/1903/
+        accept_alert { find('.js-branch-fix .btn-remove').click }
 
         expect(page).not_to have_content('fix')
         expect(find('.all-branches')).to have_selector('li', count: 0)