Fix invalid evaluation summary

WIP (#3)

* The wrong summary was used in the eval metrics.

tacotron/model.py

@@ -495,7 +495,7 @@ def model_fn(self, features, labels, mode, params):
             )
         elif mode == tf.estimator.ModeKeys.EVAL:
             eval_metrics_ops = {
-                'mean_loss': tf.metrics.mean(self.loss_op_decoder,
+                'mean_loss': tf.metrics.mean(self.loss_op,
                                              name='mean_loss'),
                 'mean_decoder_loss': tf.metrics.mean(self.loss_op_decoder,
                                                 name='mean_decoder_loss'),