fix dockerfile with a new package devs

Dockerfile

@@ -3,7 +3,7 @@ FROM alpine
 ENV GOPATH /go
 COPY . /go/src/github.com/kellegous/go
 RUN apk update \
-  && apk add go git \
+  && apk add go git musl-dev \
   && go get github.com/kellegous/go \
   && apk del go git \
   && rm -rf /var/cache/apk/* \