travis: ensure author and committer get notifications
travis: ensure author and committer get notifications

From the travis docs[1]:

"The default can be overridden in the .travis.yml ... If there's a setting
specified, Travis CI only sends an emails to the addresses specified there,
rather than to the committer and author."

So change .travis.yml to allow author and committer to receive
notifications.

[1]http://docs.travis-ci.com/user/notifications/

gonum/gonum,gonum/gonum,gonum/gonum