Make final docker image smaller

Dockerfile

@@ -1,8 +1,15 @@
-FROM gliderlabs/alpine:3.4
+FROM alpine:3.9 as builder
-RUN \
+RUN apk add --no-cache build-base
-      apk add --no-cache make gcc git libc-dev && \
+ADD endlessh.c Makefile /
-      git clone https://github.com/skeeto/endlessh && \
+RUN make
-      cd endlessh && \
+
-      make
+
+FROM alpine:3.9
+
+COPY --from=builder /endlessh /
+
 EXPOSE 2222/tcp
-ENTRYPOINT /endlessh/endlessh
+
+ENTRYPOINT ["/endlessh"]
+
+CMD ["-v"]