Fix text confirming investment heading support

We accidentally removed the `count` option in commit 55fb14ac, which
made the translation return a hash.

The test is a bit hacky, which makes me think changing the user
interface would probably be a better solution.

app/views/budgets/investments/_votes.html.erb

@@ -20,7 +20,7 @@
           method: "post",
           remote: (display_support_alert?(investment) ? false : true),
           data:   (display_support_alert?(investment) ? {
-                  confirm: t("budgets.investments.investment.confirm_group") } : nil),
+                  confirm: t("budgets.investments.investment.confirm_group", count: investment.group.max_votable_headings) } : nil),
           "aria-hidden" => css_for_aria_hidden(reason) do %>
         <%= t("budgets.investments.investment.give_support") %>
       <% end %>

config/locales/en/budgets.yml

@@ -137,7 +137,7 @@ en:
         support_title: Support this project
         confirm_group:
           one: "You can only support investments in %{count} district. If you continue you cannot change the election of your district. Are you sure?"
-          other: "You can only support investments in %{count} district. If you continue you cannot change the election of your district. Are you sure?"
+          other: "You can only support investments in %{count} districts. If you continue you cannot change the election of your district. Are you sure?"
         supports:
           one: 1 support
           other: "%{count} supports"

spec/features/budgets/votes_spec.rb

@@ -191,6 +191,13 @@ describe "Votes" do
                                          "Share it!"
       end
 
+      scenario "Confirm message shows the right text", :js do
+        visit budget_investments_path(budget, heading_id: new_york.id)
+        find(".in-favor a").click
+
+        expect(page.driver.send(:find_modal).text).to match "You can only support investments in 2 districts."
+      end
+
     end
   end
 end