added googlebot, bingbot, yandex to list of user agents for new Dynamic Rendering

Author: thoop

lib/prerender_rails.rb

@@ -4,13 +4,10 @@ class Prerender
     require 'active_support'
 
     def initialize(app, options={})
-      # googlebot, yahoo, and bingbot are not in this list because
-      # we support _escaped_fragment_ and want to ensure people aren't
-      # penalized for cloaking.
       @crawler_user_agents = [
-        # 'googlebot',
-        # 'yahoo',
-        # 'bingbot',
+        'googlebot',
+        'yahoo',
+        'bingbot',
         'baiduspider',
         'facebookexternalhit',
         'twitterbot',