change "visitor" trust level to "new user"

I blame me for this mistake.. visitor means other stuff in practice. New
User is correct meaning.

lib/promotion.rb

@@ -21,7 +21,7 @@ class Promotion
     false
   end
 
-  def review_visitor
+  def review_newuser
     return false if @user.topics_entered < SiteSetting.basic_requires_topics_entered
     return false if @user.posts_read_count < SiteSetting.basic_requires_read_posts
     return false if (@user.time_read / 60) < SiteSetting.basic_requires_time_spent_mins