Update Travis CI configuration
Update Travis CI configuration

* Use Ubuntu 14.04 with Docker.
* Use latest patch versions of Go.
* Replace hacks for forks with an official solution.
adfinis-forks/aptly,aptly-dev/aptly,aptly-dev/aptly,adfinis-forks/aptly,smira/aptly,aptly-dev/aptly,adfinis-forks/aptly,smira/aptly,smira/aptly