Rename variables describing poll options as answers

Since we've renamed the class to `Option`, having variables, methods and
texts refering to it as `answer` was confusing.

spec/system/admin/poll/polls_spec.rb

@@ -119,7 +119,7 @@ describe "Admin polls", :admin do
       expect(page).to have_content("There are no polls.")
     end
 
-    scenario "Can destroy poll with questions and answers" do
+    scenario "Can destroy poll with questions and options" do
       poll = create(:poll, name: "Do you support CONSUL?")
       create(:poll_question, :yes_no, poll: poll)