Remove to_sym from condition creation

This prevents a DoS http://www.tricksonrails.com/2010/06/avoid-memory-leaks-in-ruby-rails-code-and-protect-against-denial-of-service/

lib/liquid/tags/if.rb

@@ -63,7 +63,7 @@ module Liquid
           raise(SyntaxError.new(options[:locale].t("errors.syntax.if"))) unless expressions.shift.to_s =~ Syntax
 
           new_condition = Condition.new($1, $2, $3)
-          new_condition.send(operator.to_sym, condition)
+          new_condition.send(operator, condition)
           condition = new_condition
         end