switch to bci base image (#16)

Dockerfile

@@ -1,6 +1,6 @@
-ARG UBI_IMAGE=registry.access.redhat.com/ubi7/ubi-minimal:latest
+ARG BCI_IMAGE=registry.suse.com/bci/bci-base:latest
 ARG GO_IMAGE=rancher/hardened-build-base:v1.17.13b7
-FROM ${UBI_IMAGE} as ubi
+FROM ${BCI_IMAGE} as bci
 FROM ${GO_IMAGE} as builder
 # setup required packages
 RUN set -x \
@@ -40,8 +40,6 @@ RUN if [ "${ARCH}" != "s390x" ]; then \
 RUN install -s bin/* /usr/local/bin
 RUN metrics-server --help
 
-FROM ubi
-RUN microdnf update -y && \
-    rm -rf /var/cache/yum
+FROM bci
 COPY --from=builder /usr/local/bin/metrics-server /
 ENTRYPOINT ["/metrics-server"]