Update attention model to use tf.contrib.seq2seq.AttentionWrapper. Also Fix NaN loss issue
Update attention model to use tf.contrib.seq2seq.AttentionWrapper. Also Fix NaN loss issue

tensorflow/tensor2tensor,rsepassi/tensor2tensor,rsepassi/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,rsepassi/tensor2tensor,tensorflow/tensor2tensor,rsepassi/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor