etcd: format import order

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

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

client/v3/retry_interceptor_test.go

@@ -1,10 +1,12 @@
 package clientv3
 
 import (
+	"testing"
+
+	grpccredentials "google.golang.org/grpc/credentials"
+
 	"go.etcd.io/etcd/api/v3/v3rpc/rpctypes"
 	"go.etcd.io/etcd/client/v3/credentials"
-	grpccredentials "google.golang.org/grpc/credentials"
-	"testing"
 )
 
 type dummyAuthTokenBundle struct{}