feat(docker-kubectl): update docker and kubectl version

update docker and kubectl version

Signed-off-by: mritd <mritd@linux.com>

Author: mritd

docker-kubectl/Dockerfile

@@ -1,12 +1,12 @@
-FROM docker:19.03.12
+FROM docker:20
 
 LABEL maintainer="mritd <mritd@linux.com>"
 
 ARG TZ="Asia/Shanghai"
 
 ENV TZ ${TZ}
 
-ENV KUBE_VERSION v1.18.5
+ENV KUBE_VERSION v1.21.1
 ENV KUBECTL_DOWNLOAD_URL https://storage.googleapis.com/kubernetes-release/release/${KUBE_VERSION}/bin/linux/amd64/kubectl
 
 RUN apk upgrade --update \