Improved docker build process

Dockerfile

@@ -16,9 +16,12 @@ RUN CGO_ENABLED=0 make local build
 
 # Choose alpine as a base image to make this useful for CI, as many
 # CI tools expect an interactive shell inside the container
-FROM alpine:3.7
+FROM alpine:3.7 as production
 
 COPY --from=builder /go/src/mikefarah/yq/yq /usr/bin/yq
 RUN chmod +x /usr/bin/yq
 
+ARG VERSION=none
+LABEL version=${VERSION}
+
 WORKDIR /workdir