TF autograph compilation issue with BiLSTM embeddings

[dpressel]

While testing the dependency parser, I was using a combination of word, POS and char-lstm embeddings and it was failing with an autograph error. In most other cases when we need character composition we use dos Santos/Kim-style char conv embeddings, so Im guessing it may be a problem elsewhere. When I changed the feature to conv compositional embeddings it started working