Fix invalid postal code message

We were using the word "registered" in English as an equivalent of the
Spanish word "empadronado". However, the term "registered" is very
confusing because it might be understood as being registered in the
CONSUL website.

In the message, we're saying "cannot participate" in order to make the
message consistent with the message regarding the required age.

spec/system/verification/residence_spec.rb

@@ -108,7 +108,7 @@ describe "Residence" do
 
     click_button "Verify residence"
 
-    expect(page).to have_content "In order to be verified, you must be registered"
+    expect(page).to have_content "Citizens from this postal code cannot participate"
   end
 
   scenario "Error on census" do