appengine_flexible/redis: use new redigo dep path
appengine_flexible/redis: use new redigo dep path

Fixes #421.

GoogleCloudPlatform/golang-samples,adamyanliev/golang-samples,adamyanliev/golang-samples,GoogleCloudPlatform/golang-samples,GoogleCloudPlatform/golang-samples,adamyanliev/golang-samples,adamyanliev/golang-samples