Fix tablerow block to work with collection names in quoted syntax.

* Allows e.g. {% tablerow product in collections['frontpage'] %} instead of only collections.frontpage

lib/liquid/htmltags.rb

@@ -1,6 +1,6 @@
 module Liquid
   class TableRow < Block
-    Syntax = /(\w+)\s+in\s+(#{VariableSignature}+)/
+    Syntax = /(\w+)\s+in\s+(#{QuotedFragment}+)/
 
     def initialize(tag_name, markup, tokens)
       if markup =~ Syntax