(https://godoc.org/github.com/tensorflow/tensorflow/tensorflow/go)
*   New checkpoint format becomes the default in `tf.train.Saver`. Old V1
    checkpoints continue to be readable; controlled by the `write_version`
    argument, `tf.train.Saver` now by default writes out in the new V2 format.
    It significantly reduces the peak memory required and latency incurred
    during restore.