Prevent some random build failures when connectivity fails, by calling travis_retry which retries up to 3 times

https://travis-ci.org/piwik/piwik/jobs/23570274
https://travis-ci.org/piwik/piwik/jobs/23912462
http://blog.travis-ci.com/2013-05-20-network-timeouts-build-retries/
Updating comment to reference to ./console core:archive instead of archive.php
Prevent some random build failures when connectivity fails, by calling travis_retry which retries up to 3 times

https://travis-ci.org/piwik/piwik/jobs/23570274
https://travis-ci.org/piwik/piwik/jobs/23912462
http://blog.travis-ci.com/2013-05-20-network-timeouts-build-retries/