Release v0.13.0

- Drops Node v0.8.x support
- Updates Terraform to v0.8.0
- Restores `-b` tests
- Adds `.sass` tests

Try it out:

```
git fetch origin
git checkout -b release-v0.13.0 origin/release-v0.13.0
./bin/harp init -b hb-default-sass my-app
./bin/harp server my-app
```