Update .travis.yml for latest conventions, use fast_finish, test with -race. (#279)
Update .travis.yml for latest conventions, use fast_finish, test with -race. (#279)

* Update .travis.yml for latest conventions, use fast_finish, test with -race.

This change follows #277, but updates .travis.yml to use latest
conventions as documented at https://docs.travis-ci.com/user/languages/go#Specifying-a-Go-version-to-use.
Specifically, use master instead of tip to refer to latest (unreleased)
version of Go.

Use .x to target latest patch releases of each point release of Go.

Use fast_finish to speed up build reporting with no semantic change.
It's documented at https://blog.travis-ci.com/2013-11-27-fast-finishing-builds/.

Use race detector when running tests.

* Update .travis.yml to migrate from legacy to container-based infrastructure.

If lint doesn't do anything that would require sudo access,
it's a good idea not to require sudo access. This allows the builds
to run on Travis' newer container-based infrastructure, which
are not considered legacy and should run faster.
See https://docs.travis-ci.com/user/migrating-from-legacy/ for details.

golang/lint