Setup Travis CI

I've added a basic Travis YAML file that will build against OpenJDK 7
and Oracle JDK 8 as those are the two JDK versions we're using.

I've also setup three separate build tasks.

- `lein test` to run our automated tests
- `lein whitespace-linter`
- `lein whitespace-linter {src,test}/**/*`

The latter two, I need to add something like `|| true` to make sure the
build doesn't fail. The idea is to make sure we're eating our own dog
food.

I'll fix up the dogfooding step by ignoring the fixtures that
intentionally cause failures.