Migrate away from using io/ioutil.

[jameycribbs]

io/ioutil is deprecated in Go 1.16. Any code that uses code from this package needs to be changed to handle this. I think that Hare only uses ReadDir, but that will need to be confirmed.

Note from Go 1.16 changelog:

ReadDir => os.ReadDir (note: returns a slice of os.DirEntry rather than a slice of fs.FileInfo)

[softwarespot]

I would be happy to do this. Are you OK with that?

[mkalus]

Looks easy enough - care if I create a PR?