Revert "Update reference to ActionView::Template::Handler since it wa…

…s removed from rails"

This reverts commit 41be859.

This and the previous reverted commit broke compatibility with old Rails
versions, and didn't seem to fix anything anyway (stable, for instance, was
working just fine on new Rails versions).

What's more, Rails compatibility changes belong in stable.

lib/haml/template.rb

@@ -54,7 +54,7 @@ def precompiled_method_return_value_with_haml_xss
 # Patching was necessary for versions <= 2.0.1,
 # but we can make it a normal handler for higher versions.
 if defined?(ActionView::TemplateHandler) ||
-    (defined?(ActionView::Template) && defined?(ActionView::Template::Handlers))
+    (defined?(ActionView::Template) && defined?(ActionView::Template::Handler))
   require 'haml/template/plugin'
 else
   require 'haml/template/patch'