fix docker build for arm, amd, arm64

Dockerfile

@@ -0,0 +1,19 @@
+FROM golang:1-alpine AS build-env
+
+RUN apk add git
+
+RUN mkdir /app
+COPY . /app
+
+WORKDIR /app
+
+RUN go build -o /tmp/groxy ./cmd/groxy
+
+FROM alpine:latest
+
+COPY --from=build-env /tmp/groxy /bin/groxy
+
+RUN ls /bin/groxy
+
+CMD ["/bin/groxy"]
+