ignore: need to ensure a linebreak

If `.gitignore` does not include a linebreak (because I forgot...), the `git ignore xxx/` will include the new ignore pattern at the end _without_ a leinreak inbetween:

This `.gitignore`:

```
pattern/
# no linebreak at the end of the file
```

```
git ignore build/
```

will result in:

```
pattern/build/
# linbreak
```
