Dockerfile: use multiple stage build to reduce image size

Fix: DyegoCosta#17
Signed-off-by: CooperLi <[email protected]>

Dockerfile

@@ -1,11 +1,15 @@
-FROM golang:alpine
+FROM golang:alpine as builder
 ENV LANG en_US.UTF-8
 
-COPY . /go/src/github.com/dyegocosta/snake-game
 WORKDIR /go/src/github.com/dyegocosta/snake-game
+COPY . .
 
 RUN apk add --no-cache git
 RUN go get ./
-RUN go build -o ./_bin/snake-game
+RUN go build -ldflags="-extldflags=-static" -o /go/bin/snake-game
 
-ENTRYPOINT "./_bin/snake-game"
+FROM scratch
+WORKDIR /
+COPY --from=builder /go/bin/snake-game .
+
+ENTRYPOINT ["./snake-game"]