"invalid skaffold config" error with multi-node minikube cluster

1. create a multi-node minikube cluster using `minikube start --nodes 2`
2. run `skaffold dev`

### Expected behavior

It should work as expected

### Actual behavior

It failed with following message:

```
invalid skaffold config: getting minikube env: running [/usr/local/bin/minikube docker-env --shell none -p minikube]
- stdout: "\n\n"
- stderr: "X Exiting due to ENV_MULTINODE_CONFLICT: The docker-env command is incompatible with multi-node clusters. Use the 'registry' add-on: https://minikube.sigs.k8s.io/docs/handbook/registry/\n"
- cause: exit status 81
```

### Information

- Skaffold version: v1.20.0
- Operating system: CentOS 7
- Installed via: skaffold.dev

### Steps to reproduce the behavior

1. a clonable repository with the sample skaffold project
2. `minikube start --nodes 2`
3. `skaffold dev`