change over to upstream golang alpine image, a little less painful

Dockerfile

@@ -1,19 +1,7 @@
-FROM alpine:3.4
+FROM golang:1.7.1-alpine
 
-#RUN apk add --no-cache --repository http://dl-3.alpinelinux.org/alpine/edge/community/ go=1.7.1-r0
+RUN apk add --no-cache git
 
-RUN apk add --no-cache binutils curl git
-
-RUN cd /tmp && \
-    curl -o go1.7.1.linux-amd64.tar.gz "https://storage.googleapis.com/golang/go1.7.1.linux-amd64.tar.gz" && \
-    tar xzf go1.7.1.linux-amd64.tar.gz && \
-    rm -f go1.7.1.linux-amd64.tar.gz
-
-RUN mkdir -p /tmp/gopath && \
-    mkdir -p /tmp/ecs-discoverer
-
-ENV PATH "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/tmp/go/bin"
-
-ENV GOPATH "/tmp/gopath"
+RUN mkdir -p /tmp/ecs-discoverer
 
 COPY . /tmp/ecs-discoverer