fix(Dockerfile): Build stripe-mock binary inside docker instead of copying from host (stripe#430)

Author: ashokkjag

Dockerfile

@@ -1,8 +1,14 @@
 # -*- mode: dockerfile -*-
 
+FROM golang:alpine as builder
+WORKDIR /app
+COPY . .
+
+RUN go build -mod=vendor -o stripe-mock
+
 FROM alpine:latest
 RUN apk --no-cache add ca-certificates
-COPY stripe-mock /bin/stripe-mock
+COPY --from=builder /app/stripe-mock /bin/stripe-mock
 ENTRYPOINT ["/bin/stripe-mock", "-http-port", "12111", "-https-port", "12112"]
 EXPOSE 12111
 EXPOSE 12112