travis: removal of Python 2.6

* Removing python 2.6 from the test matrix as it times out.

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
linkbacks: fix external url creation

* Amends 4755a50867bd34a8debb4b87d952e72b931eefbc.  (addresses #1707)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>