Fix bundleExec option

The way options were being built meant the command looked like this:

```
scss-lint ./test/fixtures/valid.scss --bundle-exec
```

Rather than:

```
bundle exec scss-lint ./test/fixtures/valid.scss
```

I added a test to prove the problem and then I fixed it.

Can you merge and create a release ASAP I need this fix?

All the best,
Luke