non-existent Travis webhook auth config capability

00-fake-single.travis.yml

# ...
notifications:
  webhooks:
    url: http://your-domain.com/notifications
    auth:
      secure: "a1b2.........c3d4"

01-fake-multiple.travis.yml

# ...
notifications:
  webhooks:
    - url: http://your-domain.com/notifications
      auth:
        secure: "a1b2.........c3d4"
    - http://another-domain.com/notifications

02-fake-multiple-with-levels.travis.yml

# ...
notifications:
  webhooks:
    urls:
      - http://hooks.mydomain.com/travisci
      - url: http://your-domain.com/notifications
        auth:
          secure: "a1b2.........c3d4"
    on_success: always
    on_failure: never
    on_start: true