fix docker file

Dockerfile

@@ -1,9 +1,13 @@
 FROM golang:1.10.3-alpine as builder
 ARG GOPROXY_VERSION=master
 RUN apk update && apk upgrade && \
-    apk add --no-cache git && cd /go/src/ && git clone https://github.com/snail007/goproxy && \
-	cd goproxy && git checkout ${GOPROXY_VERSION} && \
-    go get && CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o proxy
+    apk add --no-cache git && \
+    cd /go/src/ && \
+    mkdir snail007 && \
+    cd snail007 && \
+    git clone https://github.com/snail007/goproxy.git && \
+	cd goproxy && \
+    git checkout ${GOPROXY_VERSION} && \
+    CGO_ENABLED=0 GOOS=linux go build -ldflags "-s -w" -o /proxy
 FROM alpine:3.7
-COPY --from=builder /go/src/goproxy/proxy /
 CMD /proxy ${OPTS}