Minor issue in Seq2Seq tutorial

First of all, I would like to thank you! Browsing around the net could not find a seq2seq model as clear as yours. Nonetheless, I believe there is a minor issue in ipython-notebooks/tf/TF tutorial.ipynb In [26] the line:

`dec_inp = ([tf.zeros_like(enc_inp[0], dtype=np.int32, name="GO")]+ enc_inp[:-1])`

Should be:

`dec_inp = ([tf.zeros_like(labels[0], dtype=np.int32, name="GO")] + labels[:-1])`

This will enable you to have different sequence lengths and vocab sizes for dec_inp and enc_inp.