GitLab

Changes in Tensorflow contrib:
https://github.com/tensorflow/tensorflow/commit/304faf0444260912b6996d39227417c09561c37e

Causes tensortt.py to fail. 

```
AttributeError: 'module' object has no attribute 'get_signature_def_by_key'
```
Replace `tf.contrib.saved_model.get_signature_def_by_key` with `meta_graph_def.signature_def`