Don't open auto links in a new tab

Just like we aren't opening any external links in a new tab, only, in
this case, we don't even know whether these links are internal or
external.

spec/system/comments/proposals_spec.rb

@@ -153,7 +153,7 @@ describe "Commenting proposals" do
       expect(page).to have_content "Built with http://rubyonrails.org/"
       expect(page).to have_link("http://rubyonrails.org/", href: "http://rubyonrails.org/")
       expect(find_link("http://rubyonrails.org/")[:rel]).to eq("nofollow")
-      expect(find_link("http://rubyonrails.org/")[:target]).to eq("_blank")
+      expect(find_link("http://rubyonrails.org/")[:target]).to be_blank
     end
   end