.travis.yml: generate gh-pages import redirects (#1035)
.travis.yml: generate gh-pages import redirects (#1035)

Provide the necessary Travis config to create our gh-pages site,
with import-path redirects for our packages, on pushes to master.

Taken with modifications from https://github.com/zombiezen/gg/blob/master/.travis.yml.

Requires a personal GitHub access token, which I've already set up
on the Travis settings page.

The only way to test this is to submit the PR and see what happens.
google/go-cloud,google/go-cloud,google/go-cloud