[ci skip] Use default path in button_to documentation

This is really a nit pick, but as this is the framework's documentation
I think it should follow standards as many times as possible to avoid
confusion in new users.

If we were using `resources :articles` in routes. which is what scaffold
adds, the generated helper would be `new_article_path` instead of
`new_articles_path`.

actionview/lib/action_view/helpers/url_helper.rb

@@ -253,7 +253,7 @@ module ActionView
       #   #      <input value="New" type="submit" />
       #   #    </form>"
       #
-      #   <%= button_to "New", new_articles_path %>
+      #   <%= button_to "New", new_article_path %>
       #   # => "<form method="post" action="/articles/new" class="button_to">
       #   #      <input value="New" type="submit" />
       #   #    </form>"