concatenated state will be deprecated

First thanks for this work. Works very well.
Whilst I'm testing it, it issues a warning:
```
WARNING:tensorflow:<tensorflow.python.ops.rnn_cell_impl.BasicLSTMCell object at 0x119c13748>: Using a concatenated state is slower and will soon be deprecated.  Use state_is_tuple=True.
```
tensorflow version 1.3.0
Python 3.6.2

Anyway to 'fix' it?