Add musl-dev for arm64

Dockerfile

@@ -1,7 +1,7 @@
 FROM golang:alpine AS build-env
 
 ADD . /src
-RUN apk --no-cache add git gcc
+RUN apk --no-cache add git gcc musl-dev
 RUN cd /src && go get -d && go build -o godns
 
 FROM alpine