setup Travis CI for testing

* [x] It's still necessary to [activate a webhook](http://docs.travis-ci.com/user/getting-started/) to test pull requests 
strangely that gives an error
```
can't load package: package gopkg.in/amz.v1: no buildable Go source files in /Users/nathany/src/gopkg.in/amz.v1
```

whereas `go test -v ./...` works fine.