I have a Homebrew installed kubernetes-cli 1.12.0 and minikube 0.30.0:

~ ls -l $(which kubectl)
/usr/local/bin/kubectl -> ../Cellar/kubernetes-cli/1.12.0/bin/kubectl

~ ls -l $(which minikube)
/usr/local/bin/minikube -> /usr/local/Caskroom/minikube/0.30.0/minikube-darwin-amd64


~ minikube delete
Deleting local Kubernetes cluster...
Machine deleted.
~ rm -rf ~/.kube ~/.minikube

~ minikube start --memory 8000 --kubernetes-version 1.12.0
Starting local Kubernetes 1.12.0 cluster...
Starting VM...
Downloading Minikube ISO
 170.78 MB / 170.78 MB [============================================] 100.00% 0s
Getting VM IP address...
Moving files into cluster...
E1022 10:08:41.271328   44100 start.go:254] Error updating cluster:  generating kubeadm cfg: parsing kubernetes version: parsing kubernetes version: strconv.ParseUint: parsing "": invalid syntax
================================================================================
An error has occurred. Would you like to opt in to sending anonymized crash
information to minikube to help prevent future errors?
To opt out of these messages, run the command:
    minikube config set WantReportErrorPrompt false
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