Update Dockerfile

Dockerfile

@@ -3,7 +3,7 @@ RUN apk update && apk add upx
 WORKDIR /app
 COPY main.go go.mod go.sum .
 RUN go mod tidy
-RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -ldflags="-s -w" -o myurls main.go \
+RUN CGO_ENABLED=0 go build -ldflags="-s -w" -o myurls main.go \
     && upx myurls
 
 FROM scratch