tensorflow 0.12.1 failed to run NTM

Below I show I have verified I have tensorflow 0.12.1, and the error trying to run the copy task.
```
VSs-MacBook-Pro-5:NTM-tensorflow dfreelan$ python3 -c 'import tensorflow as tf; print(tf.__version__)'
0.12.1
VSs-MacBook-Pro-5:NTM-tensorflow dfreelan$ python3 main.py --task copy --is_train True
Traceback (most recent call last):
File "main.py", line 6, in
from ntm import NTM
File "/Users/dfreelan/dev/NTM-tensorflow/ntm.py", line 8, in
from tensorflow.contrib.legacy_seq2seq import sequence_loss
ImportError: No module named 'tensorflow.contrib.legacy_seq2seq'

```

Any help trying to resolve this issue would be appreciated!

Start with the import in ntm.py and the invocation in main.py: python3 main.py --task copy --is_train True. Check how TensorFlow 0.12.1 exposes sequence_loss and identify what is needed for the copy task to start without the reported ImportError.

Written by the indexing model from the issue text.