bug fixed on tf1.5

[fortunechen]

1. tf.pack ---> tf.stack 2. tf.softmax_cross_entropy_with_logits(logits, onehot_labels, name='xentropy') ---> tf.softmax_cross_entropy_with_logits(logits=logits, labels=onehot_labels, name='xentropy') 3. add conv3_3 : net = L.conv(net, name="conv3_3", kh=3, kw=3, n_out=256)