Add Travis CI integration

A simple setup to test on latest release
and one previous version of Go.

Also, run fmt and golint before testing.

.travis.yml

@@ -0,0 +1,13 @@
+dist: xenial
+git:
+  depth: 3
+language: go
+go:
+  - "1.x"
+  - "1.10.x"
+before_script:
+  - go get golang.org/x/lint/golint
+script:
+  - gofmt -d -e -l -s .
+  - golint -set_exit_status ./...
+  - go test -v ./...