Fixing the path for the string class

Author: mogox

spec/batch_parsing_spec.rb

@@ -2,7 +2,7 @@
 $: << '../lib'
 require 'ruby-hl7'
 require 'test/hl7_messages'
-require 'string'
+require 'core_ext/string'
 
 describe HL7::Message do
   context 'batch parsing' do