Merge pull request #40 from Snawoot/docker-crosscompile

fix docker build

Dockerfile

@@ -4,6 +4,7 @@ ARG GIT_DESC=undefined
 
 WORKDIR /go/src/github.com/Snawoot/dumbproxy
 COPY . .
+ARG TARGETOS TARGETARCH
 RUN GOOS=$TARGETOS GOARCH=$TARGETARCH CGO_ENABLED=0 go build -a -tags netgo -ldflags '-s -w -extldflags "-static" -X main.version='"$GIT_DESC"
 ADD https://curl.haxx.se/ca/cacert.pem /certs.crt
 RUN chmod 0644 /certs.crt