update kubectl in dapper

Dockerfile.dapper

@@ -89,7 +89,7 @@ RUN wget -O - ${!DOCKER_URL} > /usr/bin/docker && chmod +x /usr/bin/docker
 ENV YQ_URL=https://github.com/mikefarah/yq/releases/download/3.4.1/yq_linux_${ARCH}
 RUN wget -O - ${YQ_URL} > /usr/bin/yq && chmod +x /usr/bin/yq
 
-ENV KUBECTL_URL=https://storage.googleapis.com/kubernetes-release/release/v1.11.0/bin/linux/${ARCH}/kubectl
+ENV KUBECTL_URL=https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/${ARCH}/kubectl
 RUN wget -O - ${KUBECTL_URL} > /usr/bin/kubectl && chmod +x /usr/bin/kubectl
 
 RUN apt-get update && \