SocketIO: Use better enclosing element

lib/docs/filters/socketio/clean_html.rb

@@ -2,19 +2,16 @@ module Docs
   class Socketio
     class CleanHtmlFilter < Filter
       def call
+        @doc = at_css('article')
 
         css('p > br').each do |node|
           node.remove unless node.next.content =~ /\s*\-/
         end
 
         # version documentation message
-        css('.warning').remove
+        at_css('.warning').remove
 
-        css('header').remove
-
-        css('aside').remove
-
-        css('footer').remove
+        css('header', 'footer', 'aside').remove
 
         css('pre').each do |node|
           node.content = node.content