Makefile: use Go 1.10.3 by default

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

Makefile

@@ -50,8 +50,7 @@ docker-remove:
 
 
 
-# GO_VERSION ?= 1.10.3
-GO_VERSION ?= 1.9.6
+GO_VERSION ?= 1.10.3
 ETCD_VERSION ?= $(shell git rev-parse --short HEAD || echo "GitNotFound")
 
 TEST_SUFFIX = $(shell date +%s | base64 | head -c 15)