$script.order() mutate the paths array parameter

``` JavaScript
import scriptjs from 'scriptjs';

const LIBS = ['url/to/main/lib.js', 'url/to/dep/lib.js'];

scriptjs.order(LIBS, () => done());
scriptjs.order(LIBS, () => done());
```

The second one will throw an error because `LIBS` will be mutated with the `.shift()` and will be empty.
