rockspecs: add missing YAML external library.

* lyaml-3-1.rockspec (external_dependencies): Add missing YAML.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
maint: add .travis.yml on all active branches.

* .travis.yml: Required by Travis CI to check releases.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>