Update _index.md

change version for below error
~ % minikube start -p aged --kubernetes-version=v1.16.1
😄  [aged] minikube v1.36.0 on Darwin 15.3.1 (arm64)
❗  Specified Kubernetes version 1.16.1 is less than the oldest supported version: v1.20.0. Use `minikube config defaults kubernetes-version` for details.
❗  You can force an unsupported Kubernetes version via the --force flag

❌  Exiting due to K8S_OLD_UNSUPPORTED: Kubernetes 1.16.1 is not supported by this release of minikube

Author: sannaingtun

site/content/en/docs/start/_index.md

@@ -758,7 +758,7 @@ minikube addons list
 Create a second cluster running an older Kubernetes release:
 
 ```shell
-minikube start -p aged --kubernetes-version=v1.16.1
+minikube start -p aged --kubernetes-version=v1.20.0
 ```
 
 Delete all of the minikube clusters: