Use attr_reader for warnings.

lib/liquid/tag.rb

@@ -1,6 +1,7 @@
 module Liquid
   class Tag
     attr_accessor :nodelist, :options
+    attr_reader :warnings
 
     def self.new_with_options(tag_name, markup, tokens, options)
       # Forgive me Matz for I have sinned. I know this code is weird
@@ -33,10 +34,6 @@ module Liquid
       @blank || true
     end
 
-    def warnings
-      @warnings
-    end
-
     def parse_with_selected_parser(markup)
       case @options[:error_mode] || Template.error_mode
       when :strict then strict_parse_with_error_context(markup)