Update citation HKW2014 to reflect new revision of that article on arxiv.org
Trac #16950: Update citation HKW2014 to reflect new revision of that article on arxiv.org

I have just uploaded a new revision of arxiv:1404.3680. This patch
updates the citations in the documentation of the finite state machine
module to this new revision of HKW2014.

URL: http://trac.sagemath.org/16950
Reported by: cheuberg
Ticket author(s): Clemens Heuberger
Reviewer(s): Bruno Grenet