update docker build image to go1.10.3 (#535)

Author: andrewsykim

.travis.yml

@@ -3,7 +3,7 @@ services:
 
 language: go
 go:
-  - 1.8.x
+  - 1.10.x
 
 branches:
   only: 

Makefile

@@ -17,7 +17,7 @@ DOCKER=$(if $(or $(IN_DOCKER_GROUP),$(IS_ROOT),$(OSX)),docker,sudo docker)
 MAKEFILE_DIR=$(dir $(realpath $(firstword $(MAKEFILE_LIST))))
 UPSTREAM_IMPORT_PATH=$(GOPATH)/src/github.com/cloudnativelabs/kube-router/
 BUILD_IN_DOCKER?=false
-DOCKER_BUILD_IMAGE?=golang:1.8.7-alpine
+DOCKER_BUILD_IMAGE?=golang:1.10.3-alpine
 ifeq ($(GOARCH), arm)
 ARCH_TAG_PREFIX=$(GOARCH)
 FILE_ARCH=ARM