Change some github.com urls from master to titan05

This is prompted by #803.  I did a grep through all of the docs
(recursive) for blob/master and found two hits.  A more elegant
solution would probably involve an AsciiDoc property that's centrally
controlled to avoid repetition, but with only two references, I don't
want to go overboard.  Changed both to titan05 equivalents and checked
that the links were still live.