Switch to Go 1.8

[douglas-reid]

Now that go1.8 is out and available, we should make the switch. This will require updating the runtime in our docker images, etc., and so should be done in a careful manner (perhaps following successful demo cut). This should unblock experimentation with plugins (#10) as well as other enhancements (graceful shutdown, improved gc).

[mandarjog]

Surely after the demo.
for example: golang/go#19182

[douglas-reid]

Closing. Jenkins, Travis, and bazel's rules_go have all been updated.