`preview.sh` is inaccessible under Windows by default.

- [x] I have fzf 0.30.0 or above
- [x] I have read through https://github.com/junegunn/fzf.vim/blob/master/README.md
- [x] I have read through https://github.com/junegunn/fzf/blob/master/README-VIM.md
- [x] I have read through the manual page of fzf (`man fzf`)
- [x] I have searched through the existing issues

Under Windows, I'm unable to get a preview by running the default `:Files` command.

Following further investigation, I found out that it is possible to run the `preview.sh` file but with the following modification.

`bash /mnt/c/Users/milen/.cache/dein/repos/github.com/junegunn/fzf.vim/bin/preview.sh`

In fact, anything will work when the `/mnt/c/` section is provided even with a simpler path. So the following also works.

`bash /mnt/c/Users/milen/preview.sh`

So the command(s) above are working, however the defaults are unable to execute `preview.sh`. What would be the simplest way to pass that information to `fzf.vim`.