Fix bug of training loss descent abnormal.

Fix issue #33

Author: Honghe

examples/conformer/config.yml

@@ -77,7 +77,7 @@ learning_config:
     tfrecords_dir: null
 
   optimizer_config:
-    warmup_steps: 10000
+    warmup_steps: 40000
     beta1: 0.9
     beta2: 0.98
     epsilon: 1e-9