As of a29dc8fd (2019-04-26), golang.org/x/crypto requires math/bits.
math/bits was introduced in Go 1.9, so we can no longer build from head
using 1.7.
Building using Debian's packaged dependencies should work just fine, but
since we want Travis to build from head, this commit updates the minimum
supported version to 1.9.
This patch updates the travis-ci.org configuration file to use generic Go
versions (instead of hard-coded), and Ubuntu Trusty in container mode, for
faster builds.
This commit adds a .travis.yml which configures https://travis-ci.org/, a
continuous integration service.
It only builds and runs "go test" for now because their environment is
unfortunately too old to run the integration tests.
