doxygen: Tweak the link back to ye olde Digium website

........

Merged revisions 409361 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@409362 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/asterisk.c

@@ -41,7 +41,7 @@
  *
  * Copyright (C) 1999 - 2013, Digium, Inc.
  * Asterisk is a <a href="http://www.digium.com/en/company/view-policy.php?id=Trademark-Policy">registered trademark</a>
- * of <a href="http://www.digium.com">Digium, Inc</a>.
+ * of <a rel="nofollow" href="http://www.digium.com">Digium, Inc</a>.
  *
  * \author Mark Spencer <markster@digium.com>
  * Also see \ref AstCREDITS