Adding any function to Array prototype borks Vorpal

Many packages (unfortunately) do this:

``` js
Array.prototype.pewp = function() {
return 'pewp';
}
```

Which results in:

```
rebelmail-templates$ upload-images

Invalid option: 'function () {
return 'pewp';
}'. Showing Help: function () {
return 'pewp';
}

Usage: upload-images [options] [template]

Upload images to S3.

Options:

--help output usage information
-b, --bucket S3 bucket
-a, --acl S3 ACL
function () {
return 'pewp';
}
```