bump to Go 1.9.3 for build container

CpuID · CpuID · commit a279664aa119 · 2018-02-02T11:27:43.000+10:00
diff --git a/Dockerfile b/Dockerfile
@@ -1,4 +1,4 @@
-FROM golang:1.8.1-alpine
+FROM golang:1.9.3-alpine
 
 RUN apk add --no-cache git
 
