Fix "rel" attribute in footer description links

We were accidentally filtering this attribute when sanitizing the text
since commit 928312e21.

spec/components/layout/footer_component_spec.rb

@@ -6,6 +6,7 @@ describe Layout::FooterComponent do
       render_inline Layout::FooterComponent.new
 
       page.find(".info") do |info|
+        expect(info).to have_css "a[rel=nofollow]", count: 2
         expect(info).not_to have_css "a[target]"
       end
     end