travis: set language to "shell"
travis: set language to "shell"

Travis otherwise seems to think this is a Ruby project, and if language
is set to Go it does too much fiddling with environment variables that
can't be trivially overridden.

coreos/go-systemd,endocode/go-systemd,jonboulle/go-systemd,coreos/go-systemd,endocode/go-systemd,jonboulle/go-systemd