fix docker build

Author: ochinchina

Dockerfile

@@ -1,7 +1,16 @@
-FROM golang:latest AS builder
+FROM golang:alpine AS builder
 
-ADD . /go/src/github.com/ochinchina/supervisord
-RUN go get -v -u github.com/ochinchina/supervisord && go build -o /usr/local/bin/supervisord github.com/ochinchina/supervisord
+RUN apk update && \
+    apk add git 
+
+# uncomments this if golang.org is not accessible
+#RUN mkdir -p $GOPATH/src/golang.org/x && \
+#    cd $GOPATH/src/golang.org/x && \
+#   git clone https://github.com/golang/crypto && \
+#    git clone https://github.com/golang/sys 
+
+RUN go get -v -u github.com/ochinchina/supervisord && \
+    go build -o /usr/local/bin/supervisord github.com/ochinchina/supervisord
 
 FROM alpine:latest