Changed path separator in `src_paths` when copying multiple files

Bower components may have file paths in `main` field in different formats, including `\` and `/` path separators in different cases. We can't always rely just on `path.sep` when splitting the file name prior to copying. Broken use case: with current version of `grunt-bower` copying of Twitter Bootstrap in Windows environment doesn't work, such an error is thrown:
```
Fail to copy C:/Home/edumoko/bower_components/bootstrap/dist/fonts/glyphicons-halflings-regular.ttf for bootstrap!
```

Changing the path separator to more common regexp rather than `path.sep` solves the problem.