Update /github.com/johanneswuerbach/nfsexports dependency to add LICENSE

[swinslow]

Is this a BUG REPORT or FEATURE REQUEST? (choose one): Bug Report (sort of)

What happened: /vendor/github.com/johanneswuerbach/nfsexports doesn't contain a license for that dependency. That's because the upstream project previously didn't have either a LICENSE file or a license specified in their README or source code.

They've now added an MIT license (see johanneswuerbach/nfsexports#2)

What you expected to happen: The dependency should have a license 😃

Anything else do we need to know: Can you update the version of /github.com/johanneswuerbach/nfsexports/ that minikube is using, to pull a new version that includes the LICENSE file? Nothing else should have changed in the upstream repo, so I hope that this will be a minimal update.