fix travis build

[gerbaudo]

it's also preventing the automatic generation of the doxygen docs
See last build; it seems to have broken because of this
http://docs.travis-ci.com/user/migrating-from-legacy/?utm_source=legacy-notice&utm_medium=banner&utm_campaign=legacy-upgrade

[gerbaudo]

Fixed in 1f69782; toggled permission for travis-ci application
within susynt organization and fix the link under the badge.

[gerbaudo]

Docs fixed, but still need to use the caching and re-enable the tests