etcd: format import order

golang CodeReviewComments:
https://github.com/golang/go/wiki/CodeReviewComments#imports

Signed-off-by: demoManito <1430482733@qq.com>

server/etcdserver/api/v3rpc/key_test.go

@@ -15,9 +15,10 @@
 package v3rpc
 
 import (
+	"testing"
+
 	pb "go.etcd.io/etcd/api/v3/etcdserverpb"
 	"go.etcd.io/etcd/api/v3/v3rpc/rpctypes"
-	"testing"
 )
 
 func TestCheckRangeRequest(t *testing.T) {