switch to debian:buster slim and install make

.drone.yml

@@ -16,7 +16,7 @@ steps:
   - name: dockersock
     path: /var/run
   commands:
-  - apt-get update && apt install -y --no-install-recommends curl make
+  - apt-get update && apt install -y --no-install-recommends curl make ca-certificates
   - curl -fsSLO https://download.docker.com/linux/static/stable/x86_64/docker-${DOCKERVERSION}.tgz
   - tar xzvf docker-${DOCKERVERSION}.tgz --strip 1 -C /usr/local/bin docker/docker
   - rm docker-${DOCKERVERSION}.tgz