Use JavaScript in tests opening modal dialogs

This way we reproduce the user experience in the tests, and we can make
sure modal dialogs open when we expect it.

spec/system/admin/valuator_groups_spec.rb

@@ -63,11 +63,11 @@ describe "Valuator groups", :admin do
     expect(page).to have_content "Health and Sports"
   end
 
-  scenario "Delete" do
+  scenario "Delete", :js do
     create(:valuator_group)
 
     visit admin_valuator_groups_path
-    click_link "Delete"
+    accept_confirm { click_link "Delete" }
 
     expect(page).to have_content "Valuator group deleted successfully"
     expect(page).to have_content "There are no valuator groups"