Revert "Replace on_load with instance_eval"

This reverts commit 04dfaf7.

reason: Killing the lazy-load hook obviously causes performance regressions in some cases

Author: amatsuda

lib/sprockets/railtie.rb

@@ -75,7 +75,7 @@ def configure(&block)
         app.assets.append_path path
       end
 
-      ActionView::Base.instance_eval do
+      ActiveSupport.on_load(:action_view) do
         include Sprockets::Rails::Helper
 
         # Copy relevant config to AV context