travis: Disable email notifications
travis: Disable email notifications

I'm getting spammed.  We'll see the results in the status.

Closes: #450
Approved by: jlebon

GNOME/ostree,GNOME/ostree,gatispaeglis/ostree,gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree,gatispaeglis/ostree,gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree,GNOME/ostree