Adds "Admin ballots" button in admin budgets index

spec/features/admin/budgets_spec.rb

@@ -88,6 +88,16 @@ feature "Admin budgets" do
       end
     end
 
+    scenario "Admin ballots link appears if budget has a poll associated" do
+      budget = create(:budget)
+      create(:poll, budget: budget)
+
+      visit admin_budgets_path
+
+      within "#budget_#{budget.id}" do
+        expect(page).to have_link("Admin ballots")
+      end
+    end
   end
 
   context "New" do