Use smallstep/small-cli as base image, remove step cli build

examples/docker/Makefile

@@ -2,7 +2,6 @@ all: binaries build up
 
 binaries:
 	CGO_ENABLED=0 GOOS=linux go build -o ca/step-ca github.com/smallstep/certificates/cmd/step-ca
-	CGO_ENABLED=0 GOOS=linux go build -o renewer/step github.com/smallstep/cli/cmd/step
 
 build: build-nginx build-ca build-renewer
 build-nginx:

examples/docker/renewer/Dockerfile

@@ -1,7 +1,7 @@
-FROM alpine:latest
+FROM smallstep/step-cli
 
+USER root
 RUN mkdir -p /var/local/step
-ADD step /usr/local/bin/step
 ADD crontab /var/spool/cron/crontabs/root
 RUN chmod 0644 /var/spool/cron/crontabs/root