Directory not empty error

First time I run the merge() command it merges into a new directory.
Second time I run it with the directory now existing, I get the following error:

```
Error: ENOTEMPTY: directory not empty, rmdir 'src/components'
    at Object.fs.rmdirSync (fs.js:866:18)
```

I can manually delete the directory between the 2 runs, but would be better if this is provided as an option, like "overwrite".