module: require 1.12, remove "v3" import paths

Signed-off-by: Gyuho Lee <leegyuho@amazon.com>

go.mod

@@ -1,4 +1,4 @@
-module go.etcd.io/etcd/v3
+module go.etcd.io/etcd
 
 require (
 	github.com/beorn7/perks v0.0.0-20180321164747-3a771d992973 // indirect

scripts/updatedep.sh

@@ -6,8 +6,8 @@ if ! [[ "$0" =~ scripts/updatedep.sh ]]; then
   exit 255
 fi
 
-if [[ $(go version) != "go version go1.11"* ]]; then
-  echo "expect Go 1.11+, got:" "$(go version)"
+if [[ $(go version) != "go version go1.12"* ]]; then
+  echo "expect Go 1.12+, got:" "$(go version)"
   exit 255
 fi