Don't click two places at the same time

When clicking the button "Search", the link "newest" is already present,
so capybara might click the "newest" link before the "Search" request is
finished, leading to unexpected results.

Checking the page to make sure the "Search" request has finished before
clicking the "newest" link solves the problem.

spec/features/proposals_spec.rb

@@ -1478,7 +1478,11 @@ describe "Proposals" do
       visit proposals_path
       fill_in "search", with: "Show what you got"
       click_button "Search"
+
+      expect(page).to have_content "Search results"
+
       click_link "newest"
+
       expect(page).to have_selector("a.is-active", text: "newest")
 
       within("#proposals") do