[docs] download.sh pulls from master instead of based on version tag

[cwbeitel]

I'm guessing in https://www.kubeflow.org/docs/started/getting-started-gke/ under "Deploy Kubeflow on Kubernetes Engine" the command

curl https://raw.githubusercontent.com/kubeflow/kubeflow/master/scripts/download.sh | bash

was probably meant to be a function of KUBEFLOW_TAG.

cc @sarahmaddox

[cwbeitel]

The script does the following at startup

if [ ! -z "${KUBEFLOW_VERSION}" ]; then
	KUBEFLOW_TAG=v${KUBEFLOW_VERSION}
fi

KUBEFLOW_TAG=${KUBEFLOW_TAG:-master}

suggesting the user should set KUBEFLOW_VERSION in their environment before running the script instead of KUBEFLOW_TAG (if the script is to be used as currently written).

[jlewi]

Thanks @cwbeitel