hook include of helper to loading of ActionView

When using rspec with rails-controller-testing, specs would break due to incorrect load order. More info here: rails/rails-controller-testing#24

Author: koenpunt

lib/secure_headers/view_helper.rb

@@ -108,8 +108,6 @@ def nonced_tag(type, content_or_options, block)
   end
 end
 
-module ActionView #:nodoc:
-  class Base #:nodoc:
-    include SecureHeaders::ViewHelpers
-  end
+ActiveSupport.on_load :action_view do
+  include SecureHeaders::ViewHelpers
 end