change base image version in Dockerfile.build to enable unit test in arm64 for multi-arch image issue

Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>

libnetwork/Dockerfile.build

@@ -1,4 +1,4 @@
-FROM golang:1.8.4
+FROM golang:1.8.5
 RUN apt-get update && apt-get -y install iptables
 
 RUN go get github.com/tools/godep \