Add builds for Go 1.8

[relistan]

@skey this will add a build for Go 1.8.x (picks up current latest patch level) without removing the other two builds. I'm seeing drastically shorter build times on 1.8 vs 1.7 for one of my projects.

Also worth considering adding a deploy section to the .travis.yml that will push to GitHub releases (I didn't do that here). Here's an example.

[dselans]

Yes to both. Having travis do the release would be really nice, however I've never done it. In the example you provided, there's a token in there, I assume that's encrypted?

We already have a make target for creating a semver'd release - that could probably be utilized for the travis release as well.