Mention #673 in History

Issue #673 adds a test for S3 and rubygems.org certificates to rubygems
so we can more quickly detect when a certificate's roots change.

Author: drbrain

History.txt

@@ -9,6 +9,8 @@ Bug fixes:
   change.  Fixes #665 by emeyekayee.  Fixes #671 by jonforums.
 * Remove redundant built-in certificates not needed for https://rubygems.org
   Fixes #654 by Vít Ondruch.
+* Added test for missing certificates for https://s3.amazonaws.com or
+  https://rubygems.org.  Pull request #673 by Hannes Georg.
 
 === 1.8.26 / 2013-09-24