Ruby compatibility issues

- regexp engines are different from 1.8 to 1.9, fixed the literal shorthand regexp accordingly
  - changed the shorthand regexp text from a match to a string scan
  - test_helper now loads rubygems unless RUBY_VERSION is > 1.9

lib/liquid.rb

@@ -45,7 +45,7 @@ module Liquid
   PartialTemplateParser       = /#{TagStart}.*?#{TagEnd}|#{VariableStart}.*?#{VariableIncompleteEnd}/
   TemplateParser              = /(#{PartialTemplateParser}|#{AnyStartingTag})/
   VariableParser              = /\[[^\]]+\]|#{VariableSegment}+\??/
-  LiteralShorthand            = /^(?:{{{\s?)(.*?)(?:\s*}}})$/
+  LiteralShorthand            = /^(?:\{\{\{\s?)(.*?)(?:\s*\}\}\})$/
 end
 
 require 'liquid/drop'