Go 1.10 support (#223)

* Update Travis CI to use latest Go releases

* Fix go vet issues for Go 1.10

Starting in Go 1.10, the `go test` command now automatically runs `go
vet`. This commit fixes two issues flagged by vet that cause `go test`
to fail.

* Fix gofmt issue for Go 1.10

Go 1.10 introduced a small formatting change with comments in empty
multiline slice definitions.  This commit attempts to move the offending
comment in such a way that all version of gofmt will agree on its
location.

* Remove go-vet from test.sh

Starting in Go 1.10, the `go test` command automatically runs `go vet`,
so we don't need to run `go vet` explicitly from within test.sh.

Fixes #222

.travis.yml

@@ -1,8 +1,9 @@
 sudo: false
 language: go
 go:
-  - 1.8.5
-  - 1.9.2
+  - 1.8.x
+  - 1.9.x
+  - 1.10.x
   - tip
 matrix:
   allow_failures: