Fix kwarg parsing inconsistency with Liquid::C

Liquid::C parses liquid filter arguments with dashes in them, Liquid does not.

For tags that accept kwargs and dumps them on the HTML tag, this is an important feature.

e.g. {{ ... | image_tag: loading: 'lazy', data-something: 'value!' }}

Without this change, Liquid would incorrectly parse the
`data-something` kwarg as a single argument and would skip over the
invalid characters.

See https://github.com/Shopify/theme-check/issues/539 for more context

lib/liquid.rb

@@ -36,7 +36,7 @@ module Liquid
   VariableIncompleteEnd       = /\}\}?/
   QuotedString                = /"[^"]*"|'[^']*'/
   QuotedFragment              = /#{QuotedString}|(?:[^\s,\|'"]|#{QuotedString})+/o
-  TagAttributes               = /(\w+)\s*\:\s*(#{QuotedFragment})/o
+  TagAttributes               = /(\w[\w-]*)\s*\:\s*(#{QuotedFragment})/o
   AnyStartingTag              = /#{TagStart}|#{VariableStart}/o
   PartialTemplateParser       = /#{TagStart}.*?#{TagEnd}|#{VariableStart}.*?#{VariableIncompleteEnd}/om
   TemplateParser              = /(#{PartialTemplateParser}|#{AnyStartingTag})/om