This solution has worked for me: https://github.com/helm/helm/issues/3055#issuecomment-397296485
$ kubectl create serviceaccount --namespace kube-system tiller
$ kubectl create clusterrolebinding tiller-cluster-rule --clusterrole=cluster-admin --serviceaccount=kube-system:tiller
$ helm init --service-account tiller --upgrade
$ helm update repo
$ helm install stable/redis --version 3.3.5
But after that, something has changed ; I have to add --insecure-skip-tls-verify=true flag to my kubectl commands ! I don't know how to fix that knowing that I am interacting with a gcloud containers cluster.