update dockerfile

add build flags
add upx for application compression

Dockerfile

@@ -5,7 +5,9 @@
 FROM golang:1.14-alpine
 COPY . /go/wings/
 WORKDIR /go/wings/
-RUN go build
+RUN apk add --no-cache upx \
+ && go build -ldflags="-s -w" \
+ && upx --brute wings
 
 FROM alpine:latest
 COPY --from=0 /go/wings/wings /usr/bin/