Add and apply LineContinuationSpacing rubocop rule

So now we're consistent when separating multiline strings.

spec/system/verification/level_three_verification_spec.rb

@@ -87,7 +87,7 @@ describe "Level three verification" do
 
     click_link "Send me a letter with the code"
 
-    expect(page).to have_content "Thank you for requesting your maximum security code (only required for the final votes)."\
+    expect(page).to have_content "Thank you for requesting your maximum security code (only required for the final votes)." \
                                  " In a few days we will send it to the address featuring in the data we have on file."
   end
 end